Photoelectric conversion element and solid-state imaging device

ABSTRACT

A photoelectric conversion element according to an embodiment of the present disclosure includes: a first electrode and a second electrode facing each other; and a photoelectric conversion layer provided between the first electrode and the second electrode, and including a first organic semiconductor material, a second organic semiconductor material, and a third organic semiconductor material that have mother skeletons different from one another. The first organic semiconductor material is one of fullerenes and fullerene derivatives. The second organic semiconductor material in a form of a single-layer film has a higher linear absorption coefficient of a maximal light absorption wavelength in a visible light region than a single-layer film of the first organic semiconductor material and a single-layer film of the third organic semiconductor material. The third organic semiconductor material has a value equal to or higher than a HOMO level of the second organic semiconductor material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/503,150, filed Jul. 3, 2019, now U.S. patent Ser. No. 11,056,539,which is a continuation of U.S. patent application Ser. No. 15/575,086,filed Nov. 17, 2017, now U.S. Pat. No. 10,374,015, issued Aug. 6, 2019,which is a national stage application under 35 U.S.C. 371 and claims thebenefit of PCT Application No. PCT/JP2016/064887 having an internationalfiling date of May 19, 2016, which designated the United States, whichPCT application claimed the benefit of Japanese Patent Application No.2015-110900 filed May 29, 2015, and Japanese Patent Application No.2016-072197 filed Mar. 31, 2016, the disclosures of which areincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a photoelectric conversion elementusing, for example, an organic semiconductor and a solid-state imagingdevice including the same.

BACKGROUND ART

In recent years, in solid-state imaging devices such as CCD (ChargeCoupled Device) image sensors and CMOS (Complementary Metal OxideSemiconductor) image sensors, reduction in pixel size has accelerated.The reduction in pixel size reduces the number of photons entering aunit pixel, which results in reduction in sensitivity and reduction inS/N ratio. Moreover, in a case where a color filter including atwo-dimensional array of primary-color filters of red, green, and blueis used for colorization, in a red pixel, green light and blue light areabsorbed by the color filter, which causes reduction in sensitivity.Further, in order to generate each color signal, interpolation of pixelsis performed, which causes so-called false color.

Accordingly, for example, PTL 1 discloses an image sensor using anorganic photoelectric conversion film having a multilayer configurationin which an organic photoelectric conversion film having sensitivity toblue light (B), an organic photoelectric conversion film havingsensitivity to green light (G), and an organic photoelectric conversionfilm having sensitivity to red light (R) are stacked in order. In theimage sensor, signals of B, G, and R are separately extracted from onepixel to achieve an improvement in sensitivity. PTL 2 discloses animaging element in which an organic photoelectric conversion filmconfigured of a single layer is formed, and a signal of one color isextracted from the organic photoelectric conversion film and signals oftwo colors are extracted by silicon (Si) bulk spectroscopy.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No.2003-234460

PTL 2: Japanese Unexamined Patent Application Publication No.2005-303266

SUMMARY OF THE INVENTION

In the imaging element disclosed in PTL 2, most of incident light issubjected to photoelectric conversion and is read, which results invisible light use efficiency of nearly 100%. Moreover, each lightreceiver obtains color signals of three colors R, G, and B, which makesit possible to generate an image having high sensitivity and highresolution (invisible false color). Accordingly, such a stacked imagingelement is desired to have a superior spectroscopic shape. In addition,the stacked imaging element is desired to achieve fast response time(high responsivity) necessary for rising or falling of a photocurrent inassociation with turning on or off of light, and an improvement in highexternal quantum efficiency (EQE). However, in a case where one or twocharacteristics of the spectroscopic shape, responsivity, and EQE areimproved, there is an issue that the other characteristics aredeteriorated.

It is desirable to provide a photoelectric conversion element and asolid-state imaging device that each make it possible to achieve asuperior spectroscopic shape, high responsivity, and high externalquantum efficiency.

A photoelectric conversion element according to an embodiment of thepresent disclosure includes: a first electrode and a second electrodefacing each other; and a photoelectric conversion layer provided betweenthe first electrode and the second electrode, and including a firstorganic semiconductor material, a second organic semiconductor material,and a third organic semiconductor material that have mother skeletonsdifferent from one another. The first organic semiconductor material isone of fullerenes and fullerene derivatives. The second organicsemiconductor material in a form of a single-layer film has a higherlinear absorption coefficient of a maximal light absorption wavelengthin a visible light region than a single-layer film of the first organicsemiconductor material and a single-layer film of the third organicsemiconductor material. The third organic semiconductor material has avalue equal to or higher than a HOMO level of the second organicsemiconductor material.

A solid-state imaging device according to an embodiment of the presentdisclosure includes pixels each including one or more organicphotoelectric converters, and includes the photoelectric conversionelement according to the foregoing embodiment of the present disclosureas each of the organic photoelectric converter.

In the photoelectric conversion element according to the embodiment ofthe present disclosure and the solid-state imaging device according tothe embodiment of the present disclosure, the photoelectric conversionlayer provided between the first electrode and the second electrodefacing each other is formed with use of the first organic semiconductormaterial, the second organic semiconductor material, and the thirdorganic semiconductor material that have mother skeletons different fromone another, which improves hole mobility and electron mobility in thephotoelectric conversion layer while maintaining a sharp spectroscopicshape. Moreover, electric charge transport efficiency after separationof excitons generated through light absorption into electric charges isimproved.

Herein, the first organic semiconductor material is one of fullerenesand fullerene derivatives. The second organic semiconductor material isan organic semiconductor material in a form of a single-layer filmhaving a higher linear absorption coefficient of the maximal lightabsorption wavelength in the visible light region than the single-layerfilm of the first organic semiconductor material and the single-layerfilm of the third organic semiconductor material. The third organicsemiconductor material is an organic semiconductor material having avalue equal to or higher than the HOMO level of the second organicsemiconductor material.

According to the photoelectric conversion element of the embodiment ofthe present disclosure and the solid-state imaging device of theembodiment of the present disclosure, the photoelectric conversion layeris formed with use of the first organic semiconductor material, thesecond organic semiconductor material, and the third organicsemiconductor material that have mother skeletons different from oneanother. This makes it possible to improve hole mobility and electronmobility in the photoelectric conversion layer while maintaining a sharpspectroscopic shape, thereby improving responsivity. Moreover, electriccharge transport efficiency after separation of excitons generatedthrough light absorption into electric charges is improved, which makesit possible to improve external quantum efficiency. In other words, itis possible to provide a photoelectric conversion element having asuperior spectroscopic shape, high responsivity, and high EQE, and asolid-state imaging device including the photoelectric conversionelement.

Note that effects described herein are non-limiting. An effect to beachieved by the present disclosure may be any of effects described inthe present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a schematic configuration of aphotoelectric conversion element according to an embodiment of thepresent disclosure.

FIG. 2 is a plan view of a relationship among forming positions of anorganic photoelectric conversion layer, a protective film (an upperelectrode), and a contact hole.

FIG. 3A is a cross-sectional view of a configuration example of aninorganic photoelectric converter.

FIG. 3B is another cross-sectional view of the inorganic photoelectricconverter illustrated in FIG. 3A.

FIG. 4 is a cross-sectional view of a configuration (lower-side electronextraction) of an electric charge (electron) storage layer of theorganic photoelectric converter.

FIG. 5A is a cross-sectional view for description of a method ofmanufacturing the photoelectric conversion element illustrated in FIG. 1.

FIG. 5B is a cross-sectional view of a process subsequent to the processin FIG. 5A.

FIG. 6A is a cross-sectional view of a process subsequent to the processin FIG. 5B.

FIG. 6B is a cross-sectional view of a process subsequent to the processin FIG. 6A.

FIG. 7A is a cross-sectional view of a process subsequent to the processin FIG. 6B.

FIG. 7B is a cross-sectional view of a process subsequent to the processin FIG. 7A.

FIG. 7C is a cross-sectional view of a process subsequent to the processin FIG. 7B.

FIG. 8 is a main-part cross-sectional view that describes workings ofthe photoelectric conversion element illustrated in FIG. 1 .

FIG. 9 is a schematic view for description of workings of thephotoelectric conversion element illustrated in FIG. 1 .

FIG. 10 is a functional block diagram of a solid-state imaging deviceusing the photoelectric conversion element illustrated in FIG. 1 as apixel.

FIG. 11 is a block diagram illustrating a schematic configuration of anelectronic apparatus using the solid-state imaging device illustrated inFIG. 10 .

FIG. 12 is a characteristic diagram illustrating a relationship betweeneach wavelength in a visible light region and a linear absorptioncoefficient.

MODES FOR CARRYING OUT THE INVENTION

In the following, some embodiments of the present disclosure aredescribed in detail with reference to drawings. It is to be noted thatdescription is given in the following order.

1. Embodiment (An example in which an organic photoelectric conversionlayer is formed using three kinds of materials)

1-1. Configuration of Photoelectric Conversion Element

1-2. Method of Manufacturing Photoelectric Conversion Element

1-3. Workings and Effects

2. Application Examples

3. Examples

1. EMBODIMENT

FIG. 1 illustrates a cross-sectional configuration of a photoelectricconversion element (a photoelectric conversion element 10) according toan embodiment of the present disclosure. The photoelectric conversionelement 10 configures, for example, one pixel (a unit pixel P) of asolid-state imaging device (a solid-state imaging device 1 in FIG. 10 )such as a CCD image sensor and a CMOS image sensor. In the photoelectricconversion element 10, a pixel transistor (including transfertransistors Tr1 to Tr3 to be described later) is formed and a multilayerwiring layer (a multilayer wiring layer 51) is included on a frontsurface (a surface S2 opposite to a light reception surface (a surfaceS1)) of a semiconductor substrate 11.

The photoelectric conversion element 10 according to the presentembodiment has a configuration in which one organic photoelectricconverter 11G and two inorganic photoelectric converters 11B and 11R arestacked along a vertical direction. Each of the organic photoelectricconverter 11G and the inorganic photoelectric converters 11B and 11Rselectively detects light in a relevant one of wavelength regionsdifferent from one another, and perform photoelectric conversion on thethus-detected light. The organic photoelectric converter 11G includesthree kinds of organic semiconductor materials.

(1-1. Configuration of Photoelectric Conversion Element)

The photoelectric conversion element 10 has a stacked configuration ofone organic photoelectric converter 11G and two inorganic photoelectricconverters 11B and 11R. The configuration allows one element to obtaincolor signals of red (R), green (G), and blue (B). The organicphotoelectric converter 11G is formed on a back surface (the surface S1)of the semiconductor substrate 11, and the inorganic photoelectricconverters 11B and 11R are so formed as to be embedded in thesemiconductor substrate 11. Hereinafter, description is given ofconfigurations of respective components.

(Organic Photoelectric Converter 11G)

The organic photoelectric converter 11G is an organic photoelectricconversion element that absorbs light in a selective wavelength region(green light herein) with use of an organic semiconductor to generateelectron-hole pairs. The organic photoelectric converter 11G has aconfiguration in which an organic photoelectric conversion layer 17 issandwiched between a pair of electrodes (a lower electrode 15 a and anupper electrode 18) for extraction of signal electric charges. The lowerelectrode 15 a and the upper electrode 18 are electrically coupled toconductive plugs 120 a 1 and 120 b 1 embedded in the semiconductorsubstrate 11 through wiring layers 13 a, 13 b, and 15 b and a contactmetal layer 20, as described later.

Specifically, in the organic photoelectric converter 11G, interlayerinsulating films 12 and 14 are formed on the surface S1 of thesemiconductor substrate 11, and the interlayer insulating film 12 isprovided with through holes in regions facing the respective conductiveplugs 120 a 1 and 120 b 1 to be described later. Each of the throughholes is filled with a relevant one of conductive plugs 120 a 2 and 120b 2. In the interlayer insulating film 14, wiring layers 13 a and 13 bare respectively embedded in regions facing the conductive plugs 120 a 2and 120 b 2. The lower electrode 15 a and the wiring layer 15 b areprovided on the interlayer insulating film 14. The wiring layer 15 b iselectrically isolated by the lower electrode 15 a and an insulating film16. The organic photoelectric conversion layer 17 is formed on the lowerelectrode 15 a out of the lower electrode 15 a and the wiring layer 15b, and the upper electrode 18 is so formed as to cover the organicphotoelectric conversion layer 17. As described in detail later, aprotective layer 19 is so formed on the upper electrode 18 as to cover asurface of the upper electrode 18. The protective layer 19 is providedwith a contact hole H in a predetermined region, and the contact metallayer 20 is so formed on the protective layer 19 as to be contained inthe contact hole H and to extend to a top surface of the wiring layer 15b.

The conductive plug 120 a 2 serves as a connector together with theconductive plug 120 a 1. Moreover, the conductive plug 120 a 2 forms,together with the conductive plug 120 a 1 and the wiring layer 13 a, atransmission path of electric charges (electrons) from the lowerelectrode 15 a to a green electric storage layer 110G to be describedlater. The conductive plug 120 b 2 serves as a connector together withthe conductive plug 120 b 1. Moreover, the conductive plug 120 b 2forms, together with the conductive plug 120 b 1, the wiring layer 13 b,the wiring layer 15 b, and the contact metal layer 20, a discharge pathof electric charges (holes) from the upper electrode 18. In order toallow each of the conductive plugs 120 a 2 and 120 b 2 to also serve asa light-blocking film, each of the conductive plugs 120 a 2 and 120 b 2is desirably configured of, for example, a laminated film of metalmaterials such as titanium (Ti), titanium nitride (TiN), and tungsten.Moreover, such a laminated film is desirably used, which makes itpossible to secure contact with silicon even in a case where each of theconductive plugs 120 a 1 and 120 b 1 is formed as an n-type or p-typesemiconductor layer.

The interlayer insulating film 12 is desirably configured of aninsulating film having a small interface state in order to reduce aninterface state with the semiconductor substrate 11 (a silicon layer110) and to suppress generation of a dark current from an interface withthe silicon layer 110. As such an insulating film, it is possible touse, for example, a laminated film configured of a hafnium oxide (HfO₂)film and a silicon oxide (SiO₂) film. The interlayer insulating film 14is configured of a single-layer film including one of materials such assilicon oxide, silicon nitride, and silicon oxynitride (SiON), or isconfigured of a laminated film including two or more of these materials.

The insulating film 16 is configured of, for example, a single-layerfilm including one of materials such as silicon oxide, silicon nitride,and silicon oxynitride (SiON) or a laminated film including two or moreof these materials. The insulating film 16 has, for example, aplanarized surface, thereby having a shape and a pattern that each havealmost no difference in level between the insulating film 16 and thelower electrode 15 a. In a case where the photoelectric conversionelement 10 is used as each of unit pixels P of the solid-state imagingdevice 1, the insulating film 16 has a function of electricallyisolating the lower electrodes 15 a of respective pixels from oneanother.

The lower electrode 15 a is provided in a region that faces lightreception surfaces of the inorganic photoelectric converters 11B and 11Rformed in the semiconductor substrate 11 and covers these lightreception surfaces. The lower electrode 15 a is configured of aconductive film having light transparency, and includes, for example,ITO (indium tin oxide). Alternatively, as a constituent material of thelower electrode 15 a, other than ITO, a tin oxide (SnO₂)-based materialdoped with a dopant or a zinc oxide-based material prepared by dopingaluminum zinc oxide (ZnO) with a dopant may be used. Examples of thezinc oxide-based material include aluminum zinc oxide (AZO) doped withaluminum (Al) as a dopant, gallium zinc oxide (GZO) doped with gallium(Ga), and indium zinc oxide (IZO) doped with indium (In). Moreover,other than these materials, for example, CuI, InSbO₄, ZnMgO, CuInO₂,MgIN₂O₄, CdO, or ZnSnO₃ may be used. It is to be noted that in thepresent embodiment, signal electric charges (electrons) are extractedfrom the lower electrode 15 a; therefore, in the solid-state imagingdevice 1 to be described later that uses the photoelectric conversionelement 10 as each of the unit pixels P, the lower electrode 15 a isformed separately for each of the pixels.

The organic photoelectric conversion layer 17 includes three kinds oforganic semiconductor materials, i.e., a first organic semiconductormaterial, a second organic semiconductor material, and a third organicsemiconductor material. The organic photoelectric conversion layer 17preferably includes one or both of a p-type semiconductor and an n-typesemiconductor, and one of the three kinds of organic semiconductormaterials mentioned above is the p-type semiconductor or the n-typesemiconductor. The organic photoelectric conversion layer 17 performsphotoelectric conversion on light in a selective wavelength region, andallows light in other wavelength regions to pass therethrough. In thepresent embodiment, the organic photoelectric conversion layer 17 has,for example, a maximal absorption wavelength in a range from 450 nm to650 nm both inclusive.

As the first organic semiconductor material, a material having a highelectron transporting property is preferable, and examples of such amaterial include C60 fullerene and a derivative thereof represented bythe following formula (1), and C70 fullerene and a derivative thereofrepresented by the following formula (2). It is to be noted that in thepresent embodiment, fullerenes are treated as organic semiconductormaterials.

where each R is independently one of a hydrogen atom, a halogen atom, astraight-chain, branched, or cyclic alkyl group, a phenyl group, a grouphaving a straight-chain or condensed ring aromatic compound, a grouphaving a halide, a partial fluoroalkyl group, a perfluoroalkyl group, asilylalkyl group, a silyl alkoxy group, an arylsilyl group, anarylsulfanyl group, an alkylsulfanyl group, an arylsulfonyl group, analkylsulfonyl group, an arylsulfide group, an alkylsulfide group, anamino group, an alkylamino group, an arylamino group, a hydroxy group,an alkoxy group, an acylamino group, an acyloxy group, a carbonyl group,a carboxy group, a carboxyamide group, a carboalkoxy group, an acylgroup, a sulfonyl group, a cyano group, a nitro group, a group having achalcogenide, a phosphine group, a phosphone group, and derivativesthereof, and each of “n” and “m” is 0 or an integer of 1 or more.

Specific examples of the first organic semiconductor material includenot only C60 fullerene represented by a formula (1-1) and C70 fullerenerepresented by a formula (2-1) but also compounds represented by thefollowing formulas (1-2), (1-3), and (2-2) as derivatives of C60fullerene and C70 fullerene.

Table 1 provides a summary of electron mobility of C60 fullerene (theformula (1-1)), C70 fullerene (the formula (2-1)), and the fullerenederivatives represented by the foregoing formulas (1-2), (1-3), and(2-2). Using an organic semiconductor material having high electronmobility, preferably 10⁷ cm²/Vs or more, more preferably 10 cm²/Vs ormore improves electron mobility resulting from separation of excitonsinto electric charges, and improves responsivity of the organicphotoelectric converter 11G.

TABLE 1 Electron Mobility (cm²/Vs) C60 Fullerene 2 × 10⁻² C70 Fullerene3 × 10⁻³ [60]PCBM 5 × 10⁻² [70]PCBM 3 × 10⁻⁴ ICBA 2 × 10⁻³

As the second organic semiconductor material, a material in a form of asingle-layer film having a higher linear absorption coefficient of amaximal absorption wavelength in a visible light region than asingle-layer film of the first organic semiconductor material and asingle-layer film of the third organic semiconductor material to bedescribed later is preferable. This makes it possible to enhanceabsorption capacity of light in the visible light region of the organicphotoelectric conversion layer 17 and to sharpen a spectroscopic shape.It is to be noted that the visible light region here is in a range from450 nm to 800 nm both inclusive. The single-layer film here is referredto as a single-layer film including one kind of organic semiconductormaterial. This similarly applies to the following single-layer film ineach of the second organic semiconductor material and the third organicsemiconductor material.

As the third organic semiconductor material, a material having a valueequal to or higher than a HOMO level of the second organic semiconductormaterial and having a high hole transporting property is preferable.Specifically, a material in a form of a single-layer film having higherhole mobility than hole mobility of the single-layer film of the secondorganic semiconductor material is preferable.

Specific examples of the second organic semiconductor material includesubphthalocyanine and a derivative thereof represented by a formula (6).Specific examples of the third organic semiconductor material includequinacridone and a derivative thereof represented by the followingformula (3), triallylamine and a derivative thereof represented by thefollowing formula (4), and benzothienobenzothiophene and a derivativethereof represented by a formula (5).

where each of R8 to R19 is independently selected from a groupconfigured of a hydrogen atom, a halogen atom, a straight-chain,branched, or cyclic alkyl group, a thioalkyl group, a thioaryl group, anarylsulfonyl group, an alkylsulfonyl group, an amino group, analkylamino group, an arylamino group, a hydroxy group, an alkoxy group,an acylamino group, an acyloxy group, a phenyl group, a carboxy group, acarboxyamide group, a carboalkoxy group, an acyl group, a sulfonylgroup, a cyano group, and a nitro group, any adjacent ones of R8 to R19are optionally part of a condensed aliphatic ring or a condensedaromatic ring, the condensed aliphatic ring or the condensed aromaticring optionally includes one or more atoms other than carbon, M is oneof boron and a divalent or trivalent metal, and X is an anionic group.

where each of R1 and R2 is independently one of a hydrogen atom, analkyl group, an aryl group, and a heterocyclic group, each of R3 and R4is any group and is not specifically limited, but, for example, each ofR3 and R4 is independently one of an alkyl chain, an alkenyl group, analkynyl group, an aryl group, a cyano group, a nitro group, and a silylgroup, and two or more of R3 or two or more of R4 optionally form a ringtogether, and each of n1 and n2 is independently 0 or an integer of 1 ormore.

where each of R20 to R23 is independently a substituent represented by aformula (4)′, each of R24 to R28 is independently one of a hydrogenatom, a halogen atom, an aryl group, an aromatic hydrocarbon ring group,an aromatic hydrocarbon ring group having an alkyl chain or asubstituent, an aromatic heterocyclic group, and an aromaticheterocyclic group having an alkyl chain or a substituent, adjacent onesof R24 to R28 are optionally saturated or unsaturated divalent groupsthat are bound to one another to form a ring.

where each of R5 and R6 is independently one of a hydrogen atom and asubstituent represented by a formula (5)′, and R7 is one of an aromaticring group and an aromatic ring group having a substituent.

Specific examples of the subphthalocyanine derivative represented by theformula (6) include compounds represented by the following formulas(6-1) to (6-5).

Specific examples of the quinacridone derivative represented by theformula (3) include compounds represented by the following formulas(3-1) to (3-3).

Specific examples of the triallylamine derivative represented by theformula (4) include compounds represented by the following formulas(4-1) to (4-13).

Specific examples of the benzothienobenzothiophene derivativerepresented by the formula (5) include compounds represented by thefollowing formulas (5-1) to (5-8).

Examples of the third organic semiconductor material include rubrenerepresented by the following formula (8) andN,N′-di(1-naphthyl-N,N′-diphenylbenzidine (αNPD) and a derivativethereof represented by the foregoing formula (4-2), in addition toquinacridone and the derivative thereof, triallylamine and thederivative thereof, and benzothienobenzothiophene and the derivativethereof mentioned above. Note that the third organic semiconductormaterial more preferably includes a hetero element other than carbon (C)and hydrogen (H) in a molecule of the third organic semiconductormaterial. Examples of the hetero element include nitrogen (N),phosphorus (P), and chalcogen elements such as oxygen (O), sulfur (S),and selenium (Se).

Table 2 and Table 3 provide summaries of HOMO levels (Table 2) and holemobility (Table 3) of SubPcOC₆F₅ represented by the formula (6-3) andF₆SubPcCl represented by the formula (6-2) as examples of a materialapplicable as the second organic semiconductor material, quinacridone(QD) represented by the formula (3-1), butylquinacridone (BQD)represented by the formula (3-2), αNPD represented by the formula (4-2),[1]Benzothieno[3,2-b][1]benzothiophene (BTBT) represented by the formula(5-1), and rubrene represented by the formula (8) as examples of amaterial applicable as the third organic semiconductor material, andDu-H represented by a formula (7) to be described later as a reference.It is to be noted that the HOMO level and the hole mobility provided inTables 2 and 3 are calculated with use of a method to be described inexperiments 2-1 and 2-2 of examples to be described later. The thirdorganic semiconductor material preferably has a HOMO level equal to orhigher than the HOMO level of the second organic semiconductor material.Moreover, the single-layer film of the third organic semiconductormaterial preferably has higher hole mobility than hole mobility of thesingle-layer film of the second organic semiconductor material. The HOMOlevel of the third organic semiconductor material is preferably, forexample, 10⁻⁷ cm²/Vs or more, and more preferably 10⁻⁴ cm²/Vs or more.Using such organic semiconductor materials improves hole mobilityresulting from separation of excitons into electric charges. Thisachieves balance with a high electron transporting property supported bythe first organic semiconductor material, thereby improving responsivityof the organic photoelectric converter 11G. It is to be noted that −5.5eV that is the HOMO level of QD is higher than −6.3 eV that is the HOMOlevel of F₆SubPcOCl.

TABLE 2 HOMO (eV) QD −5.5 αNPD −5.5 BTBT −5.6 SubPcOC₆F₅ −5.9 Du—H −6.1F₆SubPcCl −6.3 BQD −5.6 rubrene −5.5

TABLE 3 Hole Mobility (cm²/Vs) QD 2 × 10⁻⁵ αNPD >10⁻⁴ BTBT >10⁻³SubPcOC₆F₅ 1 × 10⁻⁸ Du—H  1 × 10⁻¹⁰ F₆SubPcCl <10⁻¹⁰ BQD 1 × 10⁻⁶rubrene 3 × 10⁻⁶

It is to be noted that in a case where the triallylamine derivative isused as the third organic semiconductor material, the triallylaminederivative is not limited to the compounds represented by the foregoingformulas (4-1) to (4-13), and may be any triallylamine derivative havinga HOMO level equal to or higher than the HOMO level of the secondorganic semiconductor material. Moreover, the triallylamine derivativemay be any triallylamine derivative that has higher hole mobility in aform of a single-layer film than hole mobility of the single-layer filmof the second organic semiconductor material.

As described above, as a specific combination of the second organicsemiconductor material and the third organic semiconductor material, forexample, in a case where the subphthalocyanine derivative is used as thesecond organic semiconductor material, one of the quinacridonederivative, the triallylamine derivative, the benzothienobenzothiophenederivative, and rubrene is selected as the third organic semiconductormaterial.

Contents of the first organic semiconductor material, the second organicsemiconductor material, and the third organic semiconductor materialconfiguring the organic photoelectric conversion layer 17 are preferablyin the following ranges. The content of the first organic semiconductormaterial is preferably, for example, in a range from 10 vol % to 35 vol% both inclusive, the content of the second organic semiconductormaterial is preferably, for example, in a range from 30 vol % to 80 vol% both inclusive, and the content of the third organic semiconductormaterial is preferably, for example, in a range from 10 vol % to 60 vol% both inclusive. Moreover, it is desirable to include substantiallyequal amounts of the first organic semiconductor material, the secondorganic semiconductor material, and the third organic semiconductormaterial. In a case where the amount of the first organic semiconductormaterial is too small, electron transporting performance of the organicphotoelectric conversion layer 17 declines, which causes a deteriorationin responsivity. In a case where the amount of the first organicsemiconductor material is too large, the spectroscopic shape may bedeteriorated. In a case where the amount of the second organicsemiconductor material is too small, light absorption capacity in thevisible light region and the spectroscopic shape may be deteriorated. Ina case where the amount of the second organic semiconductor material istoo large, electron transporting performance and hole transportingperformance decline. In a case where the amount of the third organicsemiconductor material is too small, hole transporting propertydeclines, which causes a deterioration in responsivity. In a case wherethe amount of the third organic semiconductor material is too large,light absorption capacity in the visible light region and thespectroscopic shape may be deteriorated.

Any other unillustrated layer may be provided between the organicphotoelectric conversion layer 17 and the lower electrodes 15 a andbetween the organic photoelectric conversion layer 17 and the upperelectrode 18. For example, an undercoat film, a hole transport layer, anelectron blocking film, the organic photoelectric conversion layer 17, ahole blocking film, a buffer film, an electron transport layer, and awork function adjustment film may be stacked in order from the lowerelectrode 15 a.

The upper electrode 18 is configured of a conductive film having lighttransparency as with the lower electrode 15 a. In the solid-stateimaging device using the photoelectric conversion element 10 as each ofthe pixels, the upper electrode 18 may be separately provided for eachof the pixels, or may be formed as a common electrode for the respectivepixels. The upper electrode 18 has, for example, a thickness of 10 nm to200 nm both inclusive.

The protective layer 19 includes a material having light transparency,and is, for example, a single-layer film including one of materials suchas silicon oxide, silicon nitride, and silicon oxynitride or a laminatedfilm including two or more of these materials. The protective layer 19has, for example, a thickness of 100 nm to 30000 nm both inclusive.

The contact metal layer 20 includes, for example, one of materials suchas titanium (Ti), tungsten (W), titanium nitride (TiN), and aluminum(Al), or is configured of a laminated film including two or more ofthese materials.

The upper electrode 18 and the protective layer 19 are so provided as tocover the organic photoelectric conversion layer 17, for example. FIG. 2illustrates planar configurations of the organic photoelectricconversion layer 17, the protective layer 19 (the upper electrode 18),and the contact hole H.

Specifically, an edge e2 of the protective layer 19 (and the upperelectrode 18) is located outside of an edge e1 of the organicphotoelectric conversion layer 17, and the protective layer 19 and theupper electrode 18 are so formed as to protrude toward outside of theorganic photoelectric conversion layer 17. More specifically, the upperelectrode 18 is so formed as to cover a top surface and a side surfaceof the organic photoelectric conversion layer 17, and as to extend ontothe insulating film 16. The protective layer 19 is so formed as to covera top surface of such an upper electrode 18, and is formed in a similarplanar shape to that of the upper electrode 18. The contact hole H isprovided in a region not facing the organic photoelectric conversionlayer 17 (a region outside of the edge e1) of the protective layer 19,and allows a portion of a surface of the upper electrode 18 to beexposed from the contact hole H. A distance between the edges e1 and e2is not particularly limited, but is, for example, in a range from 1 μmto 500 μm both inclusive. It is to be noted that in FIG. 2 , onerectangular contact hole H along an end side of the organicphotoelectric conversion layer 17 is provided; however, a shape of thecontact hole H and the number of the contact holes H are not limitedthereto, and the contact hole H may have any other shape (for example, acircular shape or a square shape), and a plurality of contact holes Hmay be provided.

The planarization layer 21 is so formed on the protective layer 19 andthe contact metal layer 20 as to cover entire surfaces of the protectivelayer 19 and the contact metal layer 20. An on-chip lens 22 (amicrolens) is provided on the planarization layer 21. The on-chip lens22 concentrates light incoming from a top of the on-chip lens 22 ontoeach of light reception surfaces of the organic photoelectric converter11G and the inorganic photoelectric converters 11B and 11R. In thepresent embodiment, the multilayer wiring layer 51 is formed on thesurface S2 of the semiconductor substrate 11, which makes it possible todispose the respective light reception surfaces of the organicphotoelectric converter 11G and the inorganic photoelectric converters11B and 11R close to one another. This makes it possible to reducevariation in sensitivity between respective colors caused depending onan F value of the on-chip lens 22.

It is to be noted that in the photoelectric conversion element 10according to the present embodiment, signal electric charges (electrons)are extracted from the lower electrode 15 a; therefore, in thesolid-state imaging device using the photoelectric conversion element 10as each of the pixels, the upper electrode 18 may be a common electrode.In this case, a transmission path configured of the contact hole H, thecontact metal layer 20, the wiring layers 15 b and 13 b, the conductiveplugs 120 b 1 and 120 b 2 mentioned above may be formed at least at oneposition for all pixels.

In the semiconductor substrate 11, for example, the inorganicphotoelectric converters 11B and 11R and the green electric storagelayer 110G are so formed as to be embedded in a predetermined region ofthe n-type silicon (Si) layer 110. Moreover, the conductive plugs 120 a1 and 120 b 1 configuring a transmission path of electric charges(electrons or holes) from the organic photoelectric converter 11G areembedded in the semiconductor substrate 11. In the present embodiment, aback surface (the surface S1) of the semiconductor substrate 11 servesas a light reception surface. A plurality of pixel transistors(including transfer transistors Tr1 to Tr3) corresponding to the organicphotoelectric converter 11G and the inorganic photoelectric converters11B and 11R are formed on the surface (the surface S2) side of thesemiconductor substrate 11, and a peripheral circuit including a logiccircuit, etc. is formed on the surface (the surface S2) side of thesemiconductor substrate 11.

Examples of the pixel transistor include a transfer transistor, a resettransistor, an amplification transistor, and a selection transistor.Each of these pixel transistors is configured of, for example, a MOStransistor, and is formed in a p-type semiconductor well region on thesurface S2 side. A circuit including such pixel transistors is formedfor each of photoelectric converters of red, green, and blue. Each ofthe circuits may have, for example, a three-transistor configurationincluding three transistors in total, i.e., the transfer transistor, thereset transistor, and the amplification transistor out of these pixeltransistors, or may have, for example, a four-transistor configurationfurther including the selection transistor in addition to the threetransistors mentioned above. Only the transfer transistors Tr1 to Tr3 ofthese pixel transistors are illustrated and described hereinbelow.Moreover, it is possible to share the pixel transistors other than thetransfer transistor among the photoelectric converters or among thepixels. Further, a so-called pixel sharing configuration in which afloating diffusion is shared is applicable.

The transfer transistors Tr1 to Tr3 include gate electrodes (gateelectrodes TG1 to TG3) and floating diffusions (FD 113, 114, and 116).The transfer transistor Tr1 transfers, to a vertical signal line Lsig tobe described later, signal electric charges (electrons in the presentembodiment) corresponding to green that are generated in the organicphotoelectric converter 11G and stored in the green electric storagelayer 110G. The transfer transistor Tr2 transfers, to the verticalsignal line Lsig to be described later, signal electric charges(electrons in the present embodiment) corresponding to blue that aregenerated and stored in the inorganic photoelectric converter 11B.Likewise, the transfer transistor Tr3 transfers, to the vertical signalline Lsig to be described later, signal electric charges (electrons inthe present embodiment) corresponding to red that are generated andstored in the inorganic photoelectric converter 11R.

The inorganic photoelectric converters 11B and 11R are each a photodiodehaving a p-n junction, and are formed in an optical path in thesemiconductor substrate 11 in this order from the surface S1. Theinorganic photoelectric converter 11B of the inorganic photoelectricconverters 11B and 11R selectively detects blue light and stores signalelectric charges corresponding to blue, and is so formed as to extend,for example, from a selective region along the surface S1 of thesemiconductor substrate 11 to a region in proximity to an interface withthe multilayer wiring layer 51. The inorganic photoelectric converter11R selectively detects red light and stores signal electric chargescorresponding to red, and is formed, for example, in a region below theinorganic photoelectric converter 11B (closer to the surface S2). It isto be noted that blue (B) and red (R) are, for example, a colorcorresponding to a wavelength region from 450 nm to 495 nm bothinclusive and a color corresponding to a wavelength region from 620 nmto 750 nm both inclusive, respectively, and each of the inorganicphotoelectric converters 11B and 11R may be allowed to detect light ofpart or the entirety of the relevant wavelength region.

FIG. 3A illustrates specific configuration examples of the inorganicphotoelectric converters 11B and 11R. FIG. 3B corresponds to aconfiguration in other cross-section of FIG. 3A. It is to be noted thatin the present embodiment, description is given of a case whereelectrons of electron-hole pairs generated by photoelectric conversionare read as signal electric charges (in a case where an n-typesemiconductor region serves as a photoelectric conversion layer).Moreover, in the drawings, a superscript “+(plus)” placed at “p” or “n”indicates that p-type or n-type impurity concentration is high. Further,gate electrodes TG2 and TG3 of the transfer transistors Tr2 and Tr3 outof the pixel transistors are also illustrated.

The inorganic photoelectric converter 11B includes, for example, ap-type semiconductor region (hereinafter simply referred to as p-typeregion, an n-type semiconductor region is referred in a similar manner)111 p serving as a hole storage layer and an n-type photoelectricconversion layer (an n-type region) 111 n serving as an electron storagelayer. The p-type region 111 p and the n-type photoelectric conversionlayer 111 n are formed in respective selective regions in proximity tothe surface S1, and are bent and extend to allow a portion thereof toreach an interface with the surface S2. The p-type region 111 p iscoupled to an unillustrated p-type semiconductor well region on thesurface S1 side. The n-type photoelectric conversion layer 111 n iscoupled to the FD 113 (an n-type region) of the transfer transistor Tr2for blue. It is to be noted that a p-type region 113 p (a hole storagelayer) is formed in proximity to an interface between each of ends onthe surface S2 side of the p-type region 111 p and the n-typephotoelectric conversion layer 111 n and the surface S2.

The inorganic photoelectric converter 11R is configured of, for example,p-type regions 112 p 1 and 112 p 2 (hole storage layers), and an n-typephotoelectric conversion layer 112 n (an electron storage layer)sandwiched between the p-type regions 112 p 1 and 112 p 2 (that is, hasa p-n-p laminated structure). The n-type photoelectric conversion layer112 n is bent and extends to allow a portion thereof to reach aninterface with the surface S2. The n-type photoelectric conversion layer112 n is coupled to the FD 114 (an n-type region) of the transfertransistor Tr3 for red. It is to be noted that a p-type region 113 p (ahole storage layer) is formed at least in proximity to an interfacebetween the end on the surface S2 side of the n-type photoelectricconversion layer 111 n and the surface S2.

FIG. 4 illustrates a specific configuration example of the greenelectric storage layer 110G. It is to be noted that hereinafter,description is given of a case where electrons of electrons-hole pairsgenerated by the organic photoelectric converter 11G are read as signalelectric charges from the lower electrode 15 a. Moreover, the gateelectrode TG1 of the transfer transistor Tr1 out of the pixeltransistors is also illustrated in FIG. 4 .

The green electric storage layer 110G includes an n-type region 115 nserving as an electron storage layer. A portion of the n-type region 115n is coupled to the conductive plug 120 a 1, and stores electronstransmitted from the lower electrode 15 a through the conductive plug120 a 1. The n-type region 115 n is also coupled to the FD 116 (ann-type region) of the transfer transistor Tr1 for green. It is to benoted that a p-type region 115 p (a hole storage layer) is formed inproximity to an interface between the n-type region 115 n and thesurface S2.

The conductive plugs 120 a 1 and 120 b 2 function as connectors betweenthe organic photoelectric converter 11G and the semiconductor substrate11 together with the conductive plugs 120 a 2 and 120 a 2 to bedescribed later, and configure a transmission path of electrons or holesgenerated in the organic photoelectric converter 11G. In the presentembodiment, the conductive plug 120 a 1 is brought into conduction withthe lower electrode 15 a of the organic photoelectric converter 11G, andis coupled to the green electric storage layer 110G. The conductive plug120 b 1 is brought into conduction with the upper electrode 18 of theorganic photoelectric converter 11G, and serves as a wiring line fordischarge of holes.

Each of the conductive plugs 120 a 1 and 120 b 1 is configured of, forexample, a conductive semiconductor layer, and is so formed as to beembedded in the semiconductor substrate 11. In this case, the conductiveplug 120 a 1 is of an n type (to serve as an electron transmissionpath), and the conductive plug 120 b 1 is of a p type (to serve as ahole transmission path). Alternatively, each of the conductive plugs 120a 1 and 120 b 1 is configured of, for example, a conductive filmmaterial such as tungsten (W) contained in a through via. In this case,for example, to suppress a short circuit with silicon (Si), it isdesirable to cover a via side surface with an insulating film including,for example, silicon oxide (SiO₂) or silicon nitride (SiN).

The multilayer wiring layer 51 is formed on the surface S2 of thesemiconductor substrate 11. In the multilayer wiring layer 51, aplurality of wiring lines Ma are provided with an interlayer insulatingfilm 52 in between. As described above, in the photoelectric conversionelement 10, the multilayer wiring layer 51 is formed on side opposite tothe light reception surface, which makes it possible to achieve aso-called back-side illumination type solid-state imaging device. Forexample, a supporting substrate 53 including silicon (Si) is bonded tothe multilayer wiring layer 51.

(1-2. Method of Manufacturing Photoelectric Conversion Element)

It is possible to manufacture the photoelectric conversion element 10 asfollows, for example. FIGS. 5A to 7C illustrate a method ofmanufacturing the photoelectric conversion element 10 in process order.It is to be noted that FIGS. 7A to 7C illustrate only a main-partconfiguration of the photoelectric conversion element 10.

First, the semiconductor substrate 11 is formed. Specifically, aso-called SOI substrate is prepared. In the SOI substrate, the siliconlayer 110 is formed on a silicon base 1101 with a silicon oxide film1102 in between. It is to be noted that a surface on side on which thesilicon oxide film 1102 is located, of the silicon layer 110 serves asthe back surface (the surface S1) of the semiconductor substrate 11.FIGS. 5A and 5B illustrate a state in which a configuration illustratedin FIG. 1 is vertically inverted. Next, the conductive plugs 120 a 1 and120 b 1 are formed in the silicon layer 110, as illustrated in FIG. 5A.At this occasion, through vias are formed in the silicon layer 110, andthereafter, a barrier metal such as silicon nitride described above andtungsten are contained in the through vias, which makes it possible toform the conductive plugs 120 a 1 and 120 b 1. Alternatively, aconductive extrinsic semiconductor layer may be formed by, for example,ion implantation on the silicon layer 110. In this case, the conductiveplug 120 a 1 is formed as an n-type semiconductor layer, and theconductive plug 120 b 1 is formed as a p-type semiconductor layer.Thereafter, the inorganic photoelectric converters 11B and 11R eachhaving, for example, the p-type region and the n-type region asillustrated in FIG. 3A are formed by ion implantation in regions locatedat depths different from each other in the silicon layer 110 (to besuperimposed on each other). Moreover, the green electric storage layer110G is formed by ion implantation in a region adjacent to theconductive plug 120 a 1. Thus, the semiconductor substrate 11 is formed.

Subsequently, the pixel transistors including the transfer transistorsTr1 to Tr3 and peripheral circuits such as a logic circuit are formed onthe surface S2 side of the semiconductor substrate 11, and thereafter, aplurality of layers of wiring lines 51 a are formed on the surface S2 ofthe semiconductor substrate 11 with the interlayer insulating film 52 inbetween to form the multilayer wiring layer 51, as illustrated in FIG.5B. Next, the supporting substrate 53 including silicon is bonded ontothe multilayer wiring layer 51, and thereafter, the silicon base 1101and the silicon oxide film 1102 are removed from the surface S1 of thesemiconductor substrate 11 to expose the surface S1 of the semiconductorsubstrate 11.

Next, the organic photoelectric converter 11G is formed on the surfaceS1 of the semiconductor substrate 11. Specifically, first, theinterlayer insulating film 12 configured of the foregoing laminated filmincluding the hafnium oxide film and the silicon oxide film is formed onthe surface S1 of the semiconductor substrate 11, as illustrated in FIG.6A. For example, after the hafnium oxide film is formed by an ALD(atomic layer deposition) method, the silicon oxide film is formed by,for example, a plasma CVD (Chemical Vapor Deposition) method.Thereafter, the contact holes H1 a and H1 b are formed at positionsfacing the conductive plugs 120 a 1 and 120 b 1 of the interlayerinsulating film 12, and the conductive plugs 120 a 2 and 120 b 2including the foregoing material are formed so as to be contained in thecontact holes H1 a and H1 b, respectively. At this occasion, theconductive plugs 120 a 2 and 120 b 2 may be formed to protrude to aregion to be light-blocked (to cover the region to be light-blocked).Alternatively, a light-blocking layer may be formed in a region isolatedfrom the conductive plugs 120 a 2 and 120 b 2.

Subsequently, the interlayer insulating film 14 including the foregoingmaterial is formed by, for example, a plasma CVD method, as illustratedin FIG. 6B. It is to be noted that after film formation, a front surfaceof the interlayer insulating film 14 is desirably planarized by, forexample, a CMP (Chemical Mechanical Polishing) method. Next, contactholes are formed at positions facing the conductive plugs 120 a 2 and120 b 2 of the interlayer insulating film 14, and the contact holes arefilled with the foregoing material to form the wiring layers 13 a and 13b. It is to be noted that, thereafter, a surplus wiring layer material(such as tungsten) on the interlayer insulating film 14 is desirablyremoved by a CMP method or any other method. Next, the lower electrode15 a is formed on the interlayer insulating film 14. Specifically,first, the foregoing transparent conductive film is formed on the entiresurface of the interlayer insulating film 14 by, for example, asputtering method. Thereafter, a selective portion is removed with useof a photolithography method (through performing light exposure,development, post-baking, etc. on a photoresist film), for example, withuse of dry etching or wet etching to form the lower electrode 15 a. Atthis occasion, the lower electrode 15 a is formed in a region facing thewiring layer 13 a. Moreover, in processing of the transparent conductivefilm, the transparent conductive film remains also in a region facingthe wiring layer 13 b to form, together with the lower electrode 15 a,the wiring layer 15 b configuring a portion of a hole transmission path.

Subsequently, the insulating film 16 is formed. At this occasion, first,the insulating film 16 including the foregoing material is formed by,for example, a plasma CVD method on the entire surface of thesemiconductor substrate 11 to cover the interlayer insulating film 14,the lower electrode 15 a, and the wiring layer 15 b. Thereafter, theformed insulating film 16 is polished by, for example, a CMP method toexpose the lower electrode 15 a and the wiring layer 15 b from theinsulating film 16 and to reduce (desirably eliminate) a difference inlevel between the lower electrode 15 a and the insulating film 16, asillustrated in FIG. 7A.

Next, the organic photoelectric conversion layer 17 is formed on thelower electrode 15 a, as illustrated in FIG. 7B. At this occasion,pattern formation of three kinds of organic semiconductor materialsincluding the foregoing materials is performed by, for example, a vacuumdeposition method. It is to be noted that in a case where anotherorganic layer (such as an electron blocking layer) is formed above orbelow the organic photoelectric conversion layer 17 as described above,the organic layer is desirably formed continuously in a vacuum process(in-situ vacuum process). Moreover, the method of forming the organicphotoelectric conversion layer 17 is not necessarily limited to atechnique using the foregoing vacuum deposition method, and any othertechnique, for example, a print technology may be used.

Subsequently, the upper electrode 18 and the protective layer 19 areformed, as illustrated in FIG. 7C. First, the upper electrode 18including the foregoing transparent conductive film is formed on anentire substrate surface by, for example, a vacuum deposition method ora sputtering method to cover a top surface and a side surface of theorganic photoelectric conversion layer 17. It is to be noted thatcharacteristics of the organic photoelectric conversion layer 17 easilyvary by an influence of water, oxygen, hydrogen, etc.; therefore, theupper electrode 18 is desirably formed by an in-situ vacuum processtogether with the organic photoelectric conversion layer 17. Thereafter(before pattering the upper electrode 18), the protective layer 19including the foregoing material is formed by, for example, a plasma CVDmethod to cover a top surface of the upper electrode 18. Subsequently,after the protective layer 19 is formed on the upper electrode 18, theupper electrode 18 is processed.

Thereafter, selective portions of the upper electrode 18 and theprotective layer 19 are collectively removed by etching using aphotolithography method. Subsequently, the contact hole H is formed inthe protective layer 19 by, for example, etching using aphotolithography method. At this occasion, the contact hole H isdesirably formed in a region not facing the organic photoelectricconversion layer 17. Even after formation of the contact hole H, aphotoresist is removed, and cleaning using a chemical solution isperformed by a method similar to the foregoing method; therefore, theupper electrode 18 is exposed from the protective layer 19 in a regionfacing the contact hole H. Accordingly, in view of generation of a pinhole as described above, the contact hole H is desirably provided in aregion other than a region where the organic photoelectric conversionlayer 17 is formed. Subsequently, the contact metal layer 20 includingthe foregoing material is formed with use of, for example, a sputteringmethod. At this occasion, the contact metal layer 20 is formed on theprotective layer 19 to be contained in the contact hole H and extend toa top surface of the wiring layer 15 b. Lastly, the planarization layer21 is formed on the entire surface of the semiconductor substrate 11,and thereafter, the on-chip lens 22 is formed on the planarization layer21. Thus, the photoelectric conversion element 10 illustrated in FIG. 1is completed.

In the foregoing photoelectric conversion element 10, for example, asthe unit pixel P of the solid-state imaging device 1, signal electriccharges are obtained as follows. As illustrated in FIG. 8 , light Lenters the photoelectric conversion element 10 through the on-chip lens22 (not illustrated in FIG. 8 ), and thereafter, the light L passesthrough the organic photoelectric converter 11G and the inorganicphotoelectric converters 11B and 11R in this order. Each of green light,blue light, and red light of the light L is subjected to photoelectricconversion in the course of passing. FIG. 9 schematically illustrates aflow of obtaining signal electric charges (electrons) on the basis ofincident light. Hereinafter, description is given of a specific signalobtaining operation in each photoelectric converter.

(Obtaining of Green Signal by Organic Photoelectric Converter 11G)

First, green light Lg of the light L having entered the photoelectricconversion element 10 is selectively detected (absorbed) by the organicphotoelectric converter 11G to be subjected to photoelectric conversion.Electrons Eg of thus-generated electron-hole pairs are extracted fromthe lower electrode 15 a, and thereafter, the electrons Eg are stored inthe green electric storage layer 110G through a transmission path A (thewiring layer 13 a and the conductive plugs 120 a 1 and 120 a 2). Thestored electrons Eg are transferred to the FD 116 in a readingoperation. It is to be noted that holes Hg are discharged from the upperelectrode 18 through a transmission path B (the contact metal layer 20,the wiring layers 13 b and 15 b, and the conductive plugs 120 b 1 and120 b 2).

Specifically, the signal electric charges are stored as follows. Namely,in the present embodiment, a predetermined negative potential VL (<0 V)and a potential VU (<VL) lower than the potential VL are applied to thelower electrode 15 a and the upper electrode 18, respectively. It is tobe noted that the potential VL are applied to the lower electrode 15 afrom, for example, the wiring line 51 a in the multilayer wiring layer51 through the transmission path A. The potential VL is applied to theupper electrode 18 from, for example, the wiring line 51 a in themultilayer wiring layer 51 through the transmission path B. Thus, in anelectric charge storing state (an OFF state of the unillustrated resettransistor and the transfer transistor Tr1), electrons of theelectron-hole pairs generated in the organic photoelectric conversionlayer 17 are guided to the lower electrode 15 a having a relatively highpotential (holes are guided to the upper electrode 18). Thus, theelectrons Eg are extracted from the lower electrode 15 a to be stored inthe green electric storage layer 110G (more specifically, the n-typeregion 115 n) through the transmission path A. Moreover, storage of theelectrons Eg changes the potential VL of the lower electrode 15 abrought into conduction with the green electric storage layer 110G. Achange amount of the potential VL corresponds to a signal potential(herein, a potential of a green signal).

Moreover, in a reading operation, the transfer transistor Tr1 is turnedto an ON state, and the electrons Eg stored in the green electricstorage layer 110G are transferred to the FD 116. Accordingly, a greensignal based on a light reception amount of the green light Lg is readto the vertical signal line Lsig to be described later through anunillustrated other pixel transistor. Thereafter, the unillustratedreset transistor and the transfer transistor Tr1 are turned to an ONstate, and the FD 116 as the n-type region and a storage region (then-type region 115 n) of the green electric storage layer 110G are resetto, for example, a power source voltage VDD.

(Obtaining of Blue Signal and Red Signal by Inorganic PhotoelectricConverters 11B and 11R)

Next, blue light and red light of light having passed through theorganic photoelectric converter 11G are absorbed in order by theinorganic photoelectric converter 11B and the inorganic photoelectricconverter 11R, respectively, to be subjected to photoelectricconversion. In the inorganic photoelectric converter 11B, electrons Ebcorresponding to the blue light having entered the inorganicphotoelectric converter 11B are stored in the n-type region (the n-typephotoelectric conversion layer 111 n), and the stored electrons Ed aretransferred to the FD 113 in the reading operation. It is to be notedthat holes are stored in an unillustrated p-type region. Likewise, inthe inorganic photoelectric converter 11R, electrons Er corresponding tothe red light having entered the inorganic photoelectric converter 11Rare stored in the n-type region (the n-type photoelectric conversionlayer 112 n), and the stored electrons Er are transferred to the FD 114in the reading operation. It is to be noted that holes are stored in anunillustrated p-type region.

In the electric charge storing state, the negative potential VL isapplied to the lower electrode 15 a of the organic photoelectricconverter 11G, as described above, which tends to increase a holeconcentration in the p-type region (the p-type region 111 p in FIG. 2 )as a hole storage layer of the inorganic photoelectric converter 11B.This makes it possible to suppress generation of a dark current at aninterface between the p-type region 111 p and the interlayer insulatingfilm 12.

In the reading operation, as with the foregoing organic photoelectricconverter 11G, the transfer transistors Tr2 and Tr3 are turned to an ONstate, and the electrons Eb stored in the n-type photoelectricconversion layer 111 n and the electrons Er stored in the n-typephotoelectric conversion layer 112 n are transferred to the FDs 113 and114, respectively. Accordingly, a blue signal based on a light receptionamount of the blue light Lb and a red signal based on a light receptionamount of the red light Lr are read to the vertical signal line Lsig tobe described later through an unillustrated other pixel transistor.Thereafter, the unillustrated reset transistor and the transfertransistors Tr2 and Tr3 are turned to the ON state, and the FDs 113 and114 as the n-type regions are reset to, for example, the power sourcevoltage VDD.

As described above, the organic photoelectric converter 11G and theinorganic photoelectric converters 11B and 11R are stacked along thevertical direction, which makes it possible to separately detect redlight, green light, and blue light without providing a color filter,thereby obtaining signal electric charges of respective colors. Thismakes it possible to suppress light loss (a decline in sensitivity)resulting from color light absorption by the color filter and generationof false color associated with pixel interpolation processing.

(1-3. Workings and Effects)

As described above, in recent years, in solid-state imaging devices suchas CCD image sensors and CMOS image sensors, high color reproducibility,a high frame rate, and high sensitivity have been in demand. In order toachieve high color reproducibility, the high frame rate, and highsensitivity, a superior spectroscopic shape, high responsivity, and highexternal quantum efficiency (EQE) are in demand. In a solid-stateimaging device in which a photoelectric converter including an organicmaterial (an organic photoelectric converter) and a photoelectricconverter including an inorganic material such as Si (an inorganicphotoelectric converter) are stacked, the organic photoelectricconverter extracts a signal of one color, and the inorganicphotoelectric converter extracts signals of two colors, a bulk-heterostructure is used for the organic photoelectric converter. Thebulk-hetero structure makes it possible to increase an electric chargeseparation interface by co-evaporation of the p-type organicsemiconductor material and the n-type organic semiconductor material,thereby improving conversion efficiency. Hence, in a typical solid-stateimaging device, improvements in the spectroscopic shape, responsivityand EQE of the organic photoelectric converter are achieved with use oftwo kinds of materials. In an organic photoelectric converter includingtwo kinds of materials (binary system), for example, fullerenes andquinacridones or subphthalocyanines, or quinacridones andsubphthalocyanines are used.

However, in general, a material having a sharp spectroscopic shape in asolid-state film tends not to have a high electric charge transportingproperty. In order to develop a high electric charge transportingproperty with use of a molecular material, it is necessary forrespective orbitals configured of molecules to have an overlap in asolid state. In a case where interaction between the orbitals isdeveloped, a shape of an absorption spectrum in the solid state isbroadened. For example, diindenoperylenes have high hole mobility ofabout 10⁻² cm²/Vs maximum in a solid-state film thereof In particular, asolid-state film of diindenoperylenes formed at a substrate temperaturerising to 90° C. has high hole mobility, which results from change incrystallinity and orientation of diindenoperylenes. In a case where thesolid-state film is formed at a substrate temperature of 90° C., asolid-state film that allows a current to easily flow toward a directionwhere π-stacking as one kind of intermolecular interaction is formed isformed. Thus, the material having strong interaction between moleculesin a solid-state film easily develops higher electric charge mobility.

In contrast, it is known that diindenoperylenes have a sharp absorptionspectrum in a case where diindenoperylenes are dissolved in an organicsolvent such as dichloromethane, but exhibits a broad absorptionspectrum in the solid-state film thereof. It is understood that in asolution, diindenoperylenes are diluted by dichloromethane, and aretherefore in a single molecule state, whereas intermolecular interactionis developed in the solid-state film. It can be seen that a solid-statefilm having a sharp spectroscopic shape and high electric chargetransporting property is difficult in principle.

Moreover, in the organic photoelectric converter having a binarybulk-hetero structure, electric charges (holes and electrons) generatedat a P/N interface in the solid-state film are transported. The holesare transported by the p-type organic semiconductor material, and theelectrons are transported by the n-type organic semiconductor material.Accordingly, in order to achieve high responsivity, it is necessary forboth the p-type organic semiconductor material and the n-type organicsemiconductor material to have a high electric charge transportingproperty. Hence, in order to achieve both a superior spectroscopic shapeand high responsivity, it is necessary for one of the p-type organicsemiconductor material and the n-type organic semiconductor material tohave both sharp spectroscopic characteristics and high electric chargemobility. However, it is difficult to prepare a material having a sharpspectroscopic shape and a high electric charge transporting property dueto the foregoing reason, and it is difficult to achieve a superiorspectroscopic shape, high responsivity, and high EQE with use of twokinds of materials.

In contrast, in the present embodiment, the organic photoelectricconversion layer 17 is formed with use of three kinds of organicsemiconductor materials having mother skeletons different from oneanother. Specifically, the three kinds of organic semiconductormaterials are fullerene or a fullerene derivative (the first organicsemiconductor material), an organic semiconductor material (the secondorganic semiconductor material) in a form of a single-layer film havinga higher linear absorption coefficient of a maximal absorptionwavelength in the visible light region than a single-layer film of thefirst organic semiconductor material and a single-layer film of thethird organic semiconductor material, and an organic semiconductormaterial (the third organic semiconductor material) having a value equalto or higher than the HOMO level of the second organic semiconductormaterial. This makes it possible to entrust, to another material, one ofthe sharp spectroscopic shape and high electric charge mobility, whichare expected of one or both of the p-type semiconductor and the n-typesemiconductor in the binary system. Entrusting three characteristicsincluding superior spectroscopic characteristics, hole mobility, andelectron mobility to three kinds of materials, respectively, that is,functional separation makes it possible to achieve a sharp spectroscopicshape, high responsivity, and high external quantum efficiency. In otherwords, the first organic semiconductor material makes it possible toachieve high electron mobility, the second organic semiconductormaterial makes it possible to achieve high light absorption capacity anda sharp spectroscopic shape, and the third organic semiconductormaterial makes it possible to achieve high hole mobility.

As described above, in the present embodiment, the organic photoelectricconversion layer 17 is formed with use of the foregoing three kinds oforganic semiconductor materials, i.e., the first organic semiconductormaterial, the second organic semiconductor material, and the thirdorganic semiconductor material, which makes it possible to achieve thefollowing effects. The first organic semiconductor material and thethird organic semiconductor material make it possible to achieve highelectric charge mobility, thereby improving responsivity. Transportefficiency of electric charges resulting from separation of excitons atan interface formed with use of a mixture of the first organicsemiconductor material, the second organic semiconductor material, andthe third organic semiconductor material is improved to cause animprovement in external quantum efficiency. The second organicsemiconductor material makes it possible to achieve high lightabsorption capacity and a sharp spectroscopic shape. In other words, itis possible to provide a photoelectric conversion element achieving asuperior spectroscopic shape, high responsivity, and high EQE, and asolid-state imaging device including the photoelectric conversionelement.

It is to be noted that even in a case where the sharp spectroscopicshape is not necessary, the second organic semiconductor material hashigh light absorption capacity; therefore, it is expected that using thesecond organic semiconductor material together with the first organicsemiconductor material and the third organic semiconductor materialmakes it possible to achieve the organic photoelectric conversion layer17 having superior EQE and high responsivity.

Moreover, in the present embodiment, the organic photoelectricconversion layer 17 is configured with use of the foregoing three kindsof organic semiconductor materials (the first organic semiconductormaterial, the second organic semiconductor material, and the thirdorganic semiconductor material); however, the organic photoelectricconversion layer 17 may include any material other than these materials.For example, an organic semiconductor material having the same motherskeleton as that of one of the first organic semiconductor material, thesecond organic semiconductor material, and the third organicsemiconductor material and including a different substituent may be usedas a fourth organic semiconductor material.

2. APPLICATION EXAMPLES Application Example 1

FIG. 10 illustrates an entire configuration of a solid-state imagingdevice (the solid-state imaging device 1) using the photoelectricconversion element 10 described in the foregoing embodiment as the unitpixel P. The solid-state imaging device 1 is a CMOS image sensor, andincludes a pixel section 1 a as an imaging region and a peripheralcircuit section 130 in a peripheral region of the pixel section 1 a onthe semiconductor substrate 11. The peripheral circuit section 130includes, for example, a row scanning section 131, a horizontalselection section 133, a column scanning section 134, and a systemcontroller 132.

The pixel section 1 a includes, for example, a plurality of unit pixelsP (each corresponding to the photoelectric conversion element 10) thatare two-dimensionally arranged in rows and columns. The unit pixels Pare wired with pixel driving lines Lread (specifically, row selectionlines and reset control lines) for respective pixel rows, and are wiredwith vertical signal lines Lsig for respective pixel columns. The pixeldriving lines Lread transmit drive signals for signal reading from thepixels. The pixel driving lines Lread each have one end coupled tocorresponding one of output terminals, corresponding to the respectiverows, of the row scanning section 131.

The row scanning section 131 includes a shift register and an addressdecoder, etc., and is, for example, a pixel driver that drives thepixels P of the pixel section 1 a on a row basis. Signals are outputtedfrom the pixels P of a pixel row selected and scanned by the rowscanning section 131, and the thus-outputted signals are supplied to thehorizontal selection section 133 through the respective vertical signallines Lsig. The horizontal selection section 133 includes, for example,an amplifier and horizontal selection switches that are provided for therespective vertical signal lines Lsig.

The column scanning section 134 includes a shift register and an addressdecoder, etc., and drives the horizontal selection switches of thehorizontal selection section 133 in order while sequentially performingscanning of those horizontal selection switches. Such selection andscanning performed by the column scanning section 134 allow the signalsof the pixels P transmitted through the respective vertical signal linesLsig to be sequentially outputted to a horizontal signal line 135. Thethus-outputted signals are transmitted to outside of the semiconductorsubstrate 11 through the horizontal signal line 135.

A circuit portion configured of the row scanning section 131, thehorizontal selection section 133, the column scanning section 134, andthe horizontal signal line 135 may be provided directly on thesemiconductor substrate 11, or may be disposed in an external controlIC. Alternatively, the circuit portion may be provided in any othersubstrate coupled by means of a cable or any other coupler.

The system controller 132 receives, for example, a clock supplied fromthe outside of the semiconductor substrate 11 and data on instructionsof operation modes, and outputs data such as internal information of thesolid-state imaging device 1. Furthermore, the system controller 132includes a timing generator that generates various timing signals, andperforms drive control of peripheral circuits such as the row scanningsection 131, the horizontal selection section 133, and the columnscanning section 134 on the basis of the various timing signalsgenerated by the timing generator.

Application Example 2

The foregoing solid-state imaging device 1 is applicable to variouskinds of electronic apparatuses having imaging functions. Examples ofthe electronic apparatuses include camera systems such as digital stillcameras and video cameras, and mobile phones having imaging functions.FIG. 11 illustrates, for purpose of an example, a schematicconfiguration of an electronic apparatus 2 (e.g., a camera). Theelectronic apparatus 2 is, for example, a video camera that allows forshooting of a still image or a moving image. The electronic apparatus 2includes the solid-state imaging device 1, an optical system (e.g., anoptical lens) 310, a shutter unit 311, a driver 313, and a signalprocessor 312. The driver 313 drives the solid-state imaging device 1and the shutter unit 311.

The optical system 310 guides image light (i.e., incident light) from anobject toward the pixel section 1 a of the solid-state imaging device 1.The optical system 310 may include a plurality of optical lenses. Theshutter unit 311 controls a period in which the solid-state imagingdevice 1 is irradiated with the light and a period in which the light isblocked. The driver 313 controls a transfer operation of the solid-stateimaging device 1 and a shutter operation of the shutter unit 311. Thesignal processor 312 performs various signal processes on signalsoutputted from the solid-state imaging device 1. A picture signal Douthaving been subjected to the signal processes is stored in a storagemedium such as a memory, or is outputted to a unit such as a monitor.

3. EXAMPLES

Hereinafter, various samples of examples and comparative examplesrelated to the embodiment of the present disclosure and modificationexamples thereof were fabricated, and spectroscopic characteristics,HOMO levels, hole mobility, external quantum efficiency (EQE), andresponsivity of the samples were evaluated.

Experiment 1: Evaluation of Spectroscopic Characteristics

A glass substrate was cleaned by UV/ozone treatment. Quinacridone (QD;the formula (3-1)) was evaporated on the glass substrate by a resistanceheating method in a vacuum of 1×10⁻⁵ Pa or less with use of an organicevaporation apparatus while rotating a substrate holder. Evaporationspeed was 0.1 nm/sec, and a film having a total thickness of 50 nm wasformed as a sample 1. In addition, in place of using QD, a sample 2using SubPcCl (the formula (6-1)), a sample 3 using C60 (the formula(1-1)), a sample 4 using αNPD (the formula (4-2)), a sample 5 using BTBT(the formula (5-1)), a sample 59 using BQD (the formula (3-2)), and asample 60 using rubrene (the formula (8)) were fabricated, andspectroscopic characteristics of the respective samples were evaluated.

Transmittance and reflectivity for each wavelength were measured withuse of an ultraviolet-visible spectrophotometer to determineabsorptivity (%) of light aborbed by each of single-layer films as thespectroscopic characteristics. A linear absorption coefficient α (cm⁻¹)for each wavelength in each of the single-layer films was evaluated bythe Lambert-Beer law using the light absorptivity and the thickness ofthe single-layer film as parameters.

FIG. 12 illustrates a relationship between a visible light region(herein, in a range from 450 nm to 700 nm both inclusive) and the linearabsorption coefficient of the samples 1 to 5 and the samples 59 and 60.As can be seen from FIG. 12 , SubPcCl as the second organicsemiconductor material has a higher linear absorption coefficient of amaximal absorption wavelength in the visible light region, as comparedwith the other first and third organic semiconductor materials. It is tobe noted that as long as each of the organic semiconductor materials isa compound having the same mother skeleton, a tendency of the absorptioncoefficient illustrated in FIG. 12 is maintained in general.

Experiment 2-1: Evaluation of HOMO Level

The HOMO levels of the organic semiconductor materials summarized inTable 2 mentioned above were calculated from respective single-layerfilms of QD (the formula (3-1)), αNPD (the formula (4-2)), BTBT (theformula (5-1)), SubPcOC₆F₅ (the formula (6-3)), Du-H (the followingformula (7)), F₆SubPcCl (the formula (6-2)), BQD (the formula (3-2)),and rubrene (the formula (8)) with use of a method similar to that inthe experiment 1. It is to be noted that a thickness of each of therespective single-layer films including the organic semiconductormaterials was 20 nm.

The HOMO level is a value obtained as follows. Ultraviolet light of 21.2eV was applied to each of the samples to obtain a kinetic energydistribution of electrons emitted from a surface of the sample, and anenergy width of a spectrum of the kinetic energy distribution wassubtracted from an energy value of the applied ultraviolet light toobtain the HOMO level.

Experiment 2-2: Evaluation of Hole Mobility

Hole mobility of the organic semiconductor materials summarized in Table3 mentioned above was calculated from samples fabricated by thefollowing method. First, a glass substrate provided with a Pt electrodehaving a thickness of 50 nm was cleaned by UV/ozone treatment, andthereafter, a film of LiF having a total thickness of 0.5 nm was formedon the glass substrate. Subsequently, QD (the formula (3-1)) wasevaporated by a resistance heating method in a vacuum of 1×10⁻⁵ Pa orless with use of an organic evaporation apparatus while rotating asubstrate holder. Evaporation speed was 0.1 nm/sec, and a film having atotal thickness of 100 nm was formed. Next, a film of LiF having a totalthickness of 0.5 nm was formed on the glass substrate, and thereafter, afilm of Au having a thickness of 100 nm was formed by an evaporationmethod to cover a single-layer film of QD, thereby fabricating aphotoelectric conversion element having a 1-mm by 1-mm photoelectricconversion region. As other samples, in place of the single-layer filmof QD, photoelectric conversion elements including single-layer films ofαNPD (the formula (4-2)), BTBT (the formula (5-1)), SubPcOC₆F₅ (theformula (6-3)), Du-H (the formula (7)), F₆SubPcCl (the formula (6-2)),BQD (the formula (3-2)), and rubrene (the formula (8)) were fabricated,and hole mobility of each of the samples was calculated.

The hole mobility was calculated with use of a semiconductor parameteranalyzer. Specifically, a bias voltage to be applied between electrodeswas swept from 0 V to −5 V to obtain a current-voltage curve. The curvewas fit with a space charge limited current model to determine arelational expression between mobility and voltage, thereby obtaining avalue of hole mobility at −1 V.

Experiment 3: Evaluation of Spectroscopic Characteristics, ExternalQuantum Efficiency, and Responsivity Experimental Example 3-1

First, as an example (a sample 6), an organic photoelectric conversionlayer was formed as follows. A glass substrate provided with an ITOelectrode having a thickness of 50 nm was cleaned by UV/ozone treatment,and thereafter, C60 (the formula (1-1)) as the first semiconductormaterial (a first kind), SubPcOC₆F₅ (the formula (6-3)) as the secondorganic semiconductor material (a second kind), and BQD (the formula(3-2)) as the third organic semiconductor material (a third kind) wereevaporated simultaneously by a resistance heating method in a vacuum of1×10⁻⁵ Pa or less with use of an organic evaporation apparatus whilerotating a substrate holder, thereby forming the organic photoelectricconversion layer. A film of C60, a film of SubPcO₆CF₅, and a film of BQDwere formed at evaporation speed of 0.075 nm/sec, 0.075 nm/sec, and 0.05nm/sec, respectively to have a total thickness of 100 nm. Moreover, afilm of ITO having a thickness of 50 nm was formed on the organicphotoelectric conversion layer by a sputtering method to fabricate asample for evaluation of spectroscopic characteristics. Further, a filmof AlSiCu having a thickness of 100 nm was formed on the organicphotoelectric conversion layer by an evaporation method to fabricate aphotoelectric conversion element including the film of AlSiCu as anupper electrode and having a 1-mm by 1-mm photoelectric conversionregion. Furthermore, as a comparative example, a method similar to thatin the sample 6 was used to fabricate a sample 7 in which the organicphotoelectric conversion layer was formed using SubPcOC₆F₅ and BQD, asample 8 in which the organic photoelectric conversion layer was formedusing C60 and BQD, and a sample 9 in which the organic photoelectricconversion layer was formed using C60 and SubPcOC₆F₅, and spectroscopiccharacteristics, photoelectric conversion efficiency, and responsivityof each of the samples were evaluated as follows.

(Method of Evaluating Spectroscopic Characteristics)

The spectroscopic characteristics were evaluated with use of anultraviolet-visible spectrophotometer. Transmittance and reflectivityfor each wavelength were measured to determine light absorptivity (%) oflight absorbed by the organic photoelectric conversion layer, and alinear absorption coefficient α (cm⁻¹) for each wavelength in theorganic photoelectric conversion layer was evaluated by the Lambert-Beerlaw using the light absorptivity and the thickness of the organicphotoelectric conversion layer as parameters. A spectroscopiccharacteristic diagram showing a spectroscopic shape was formed on thebasis of the linear absorption coefficient α (cm⁻¹) for each wavelength,and two points of wavelength at which relative intensity was ⅓ of a peakvalue of an absorption band in the visible light region were determined,and a distance between the two points was calculated. As a indication ofpropriety of the spectroscopic shape, in a case where the distancebetween the two points is equal to or less than 115 nm, thespectroscopic shape was determined to be “Narrow”, and in a case wherethe distance between the two points was larger than 115 nm, thespectroscopic shape was determined to be “Broad”.

(Method of Evaluating External Quantum Efficiency)

External quantum efficiency was evaluated with use of a semiconductorparameter analyzer. Specifically, external quantum efficiency wascalculated from a bright current value and a dark current value in acase where an amount of light to be applied from a light source to thephotoelectric conversion element through a filter was 1.62 μW/cm², and abias voltage to be applied between electrodes was −1 V.

(Method of Evaluating Responsivity)

Responsivity was evaluated on the basis of speed of falling, afterstopping application of light, a bright current value observed duringapplication of light with use of a semiconductor parameter analyzer.Specifically, an amount of light to be applied from a light source tothe photoelectric conversion element through a filter was 1.62 μW/cm²,and a bias voltage to be applied between electrodes was −1 V. Astationary current was observed in this state, and thereafter,application of light was stopped, and how the current was attenuated wasobserved. Subsequently, a dark current value was subtracted from anobtained current-time curve. A current-time curve to be thereby obtainedwas used, and time necessary for a current value after stoppingapplication of light to attenuate to 3% of an observed current value ina stationary state was an indication of responsivity.

Moreover, as experimental examples 3-2 to 3-12, as with the foregoingexperimental example 3-1, samples 10 to 39 and samples 44 to 55 asexamples and comparative examples having other materials and otherconfigurations were fabricated, and spectroscopic characteristics,photoelectric conversion efficiency, and responsivity of each of thesesamples were evaluated. Tables 4 to 6 provide summaries ofconfigurations, spectroscopic shapes (stereoscopic characteristics),photoelectric conversion efficiency, and responsivity of the organicphotoelectric conversion layers of the samples 6 to 39 and the samples44 to 55. It is to be noted that the sample 36 is an example of aphotoelectric conversion layer including four kinds of organicsemiconductor materials that included the foregoing fourth organicsemiconductor material. Herein, as the fourth organic semiconductormaterial, one kind was further selected from the first organicsemiconductor materials. Moreover, a numerical value given in each ofthe comparative examples in Tables 4 to 6 is a relative value in a casewhere a value of the example in each material configuration was 1.0.

TABLE 4 Organic Photoelectric Characteristic Conversion LayerParticularly First Second Third Spectroscopic Inferior to Kind Kind KindShape EQE Responsivity Example Experimental Sample 6 Formula FormulaFormula Narrow 1.00 1.0 — Example 3-1 (1-1) (6-3) (3-2) 25% 37.5% 37.5%Sample 7 — Formula Formula Narrow 0.45 3.0 Response (6-3) (3-2) Speed —  50%   50% Sample 8 Formula — Formula Board 0.62 1.0 Spectroscopic(1-1) (3-2) Shape 75% —   25% Sample 9 Formula Formula — Narrow 0.37 2.0EQE (1-1) (6-3) 25%   75% — Experimental Sample 10 Formula FormulaFormula Narrow 1.00 1.0 — Example 3-2 (1-1) (6-1) (3-2) 25% 37.5% 37.5%Sample 11 — Formula Formula Narrow 0.37 4.0 Response (6-1) (3-2) Speed —  50%   50% Sample 12 Formula — Formula Board 0.70 1.0 Spectroscopic(1-1) (3-2) Shape 75% —   25% Sample 13 Formula Formula — Narrow 0.6110.0 EQE (1-1) (6-1) 25%   75% — Experimental Sample 14 Formula FormulaFormula Narrow 1.00 1.0 — Example 3-3 (1-1) (6-4) (3-2) 25% 37.5% 37.5%Sample 15 — Formula Formula Narrow 0.84 2.0 Response (6-4) (3-2) Speed —  50%   50% Sample 16 Formula — Formula Board 0.64 2.5 Spectroscopic(1-1) (3-2) Shape 75% —   25% Sample 17 Formula Formula — Narrow 0.00Undetectable EQE (1-1) (6-4) 25%   75% — Experimental Sample 18 FormulaFormula Formula Narrow 1.00 1.0 — Example 3-4 (1-1) (6-2) (3-2) 25%37.5% 37.5% Sample 19 — Formula Formula Narrow 0.92 2.0 Response (6-2)(3-2) Speed —   50%   50% Sample 20 Formula — Formula Board 0.64 3.0Spectroscopic (1-1) (3-2) Shape 75% —   25% Sample 21 Formula Formula —Narrow 0.00 Undetectable EQE (1-1) (6-2) 25%   75% —

TABLE 5 Characteristic Particularly Organic Photoelectric ConversionLayer Spectroscopic Inferior to First Kind Second Kind Third Kind ShapeEQE Responsivity Example Experimental Sample Formula (1-1) Formula (6-2)Formula (3-1) Narrow 1.00 1.0 — Example 3-5 22 25% 37.5%  37.5%  Sample— Formula (6-2) Formula (3-1) Narrow 0.85 4.0 Response Speed 23 — 50%50% Sample Formula (1-1) — Formula (3-1) Board 0.87 5.0 Spectroscopic 2425% — 75% Shape Sample Formula (1-1) Formula (6-2) — Narrow 0.00Undetectable EQE 25 25% 75% — Experimental Sample Formula (1-1) Formula(6-2) Formula (4-2) Narrow 1.00 1.0 — Example 3-6 26 25% 37.5%  37.5% Sample — Formula (6-2) Formula (4-2) Narrow 0.73 10.0  Response Speed 27— 50% 50% Sample Formula (1-1) Formula (6-2) — Narrow 0.00 UndetectableEQE 28 25% 75% — Experimental Sample Formula (1-1) Formula (6-2) Formula(5-1) Narrow 1.00 1.0 — Example 3-7 29 25% 37.5%  37.5%  Sample —Formula (6-2) Formula (5-1) Narrow 0.37 10.0  Response speed 30 — 50%50% Sample Formula (1-1) Formula (6-2) — Narrow 0.00 Undetectable EQE 3125% 75% — Experimental Sample Formula (2-1) Formula (6-3) Formula (3-2)Narrow 1.00 1.0 — Example 3-8 32 25% 37.5%  37.5%  Sample — Formula(6-3) Formula (3-2) Narrow 0.40 5.0 Response Speed 33 — 50% 50% SampleFormula (2-1) — Formula (3-2) Board 0.65 4.0 Spectroscopic 34 25% — 75%Shape Sample Formula (2-1) Formula (6-3) Narrow 0.37 8.0 EQE 35 25% 75%— Experimental Sample Formula (1-1) + Formula (6-3) Formula (3-2) Narrow1.00 1.0 — Example 3-9 36 Formula (2-1)   25% 37.5%  37.5%  Sample —Formula (6-3) Formula (3-2) Narrow 0.43 6.0 Response Speed 37 — 50% 50%Sample Formula (1-1) + — Formula (3-2) Board 0.62 4.0 Spectroscopic 38Formula (2-1)   25% — 75% Shape Sample Formula (1-1) + Formula (6-3) —Narrow 0.33 6.0 EQE 39 Formula (2-1)   25% 75% —

TABLE 6 Organic Photoelectric Characteristic Conversion LayerParticularly First Second Third Spectroscopic Inferior to Kind Kind KindShape EQE Responsivity Example Experimental Sample Formula FormulaFormula Narrow 1.00 1.0 — Example 44 (1-1) (6-2) (3-3) 3-10 25% 37.5%37.5% Sample — Formula Formula Narrow 0.64 10.0 Response 45 (6-2) (3-3)Speed —   50%   50% Sample Formula — Formula Board 0.43 20.0Spectroscopic 46 (1-1) (3-3) Shape 25% —   75% Sample Formula Formula —Narrow 0.00 Undetectable External 47 (1-1) (6-2) Quantum 25%   75% —Efficiency Experimental Sample Formula Formula Formula Narrow 1.00 1.0 —Example 48 (1-1) (6-5) (3-2) 3-11 25% 37.5% 37.5% Sample — FormulaFormula Narrow 0.84 1.8 Response 49 (6-5) (3-2) Speed —   50%   50%Sample Formula — Formula Board 0.67 2.5 Spectroscopic 50 (1-1) (3-2)Shape 25% —   75% Sample Formula Formula — Narrow 0.00 UndetectableExternal 51 (1-1) (6-5) Quantum 25%   75% — Efficiency ExperimentalSample Formula Formula — Narrow 0.00 Undetectable External Example 52(1-1) (6-5) Quantum 3-12 25% 37.5% — Efficiency Sample Formula FormulaFormula Narrow 1.00 1 — 53 (1-1) (6-2) (8) 25% 37.5% 37.5% SampleFormula — Formula Board 1.60 3 Spectroscopic 54 (1-1) (8) Shape 25% —  75% Sample Formula Formula — Narrow 0.00 Undetectable External 55(1-1) (6-2) Quantum 25%   75% — Efficiency

As can be seen from Tables 4 to 6, as compared with a sample (theexample, e.g. the sample 6) having a configuration of the photoelectricconversion element of the foregoing embodiment, in samples (thecomparative examples, e.g., the samples 7 to 9) including two kinds oforganic semiconductor materials selected from the three kinds of organicsemiconductor materials used in the sample 6, one characteristic of thespectroscopic shape, response speed, and EQE was inferior. In otherwords, it was found that the organic photoelectric conversion layerconfigured using three kinds of organic semiconductor materials made itpossible to achieve a superior spectroscopic shape, high response speed,and high EQE.

Experiment 4: Regarding Composition Ratio and Combination of OrganicSemiconductor Materials Experimental Examples 4-1 to 4-3

In an experimental example 4-1, samples 61, 40, and 41 in which thecomposition ratio of the first organic semiconductor material, thesecond organic semiconductor material, and the third organicsemiconductor material was changed were fabricated, and spectroscopiccharacteristics, photoelectric conversion efficiency, and responsivityof each of the samples were evaluated. In an experimental example 4-2, aphotoelectric conversion element that included an organic photoelectricconversion layer using, as the second organic semiconductor material, amaterial (the formula (4-2)) in a form of a single-layer film having alower linear absorption coefficient of a maximal absorption wavelengthin the visible light region than a single-layer film of the firstorganic semiconductor material and a single-layer film of the thirdorganic semiconductor material to be described later was fabricated (asample 42), and spectroscopic characteristics, photoelectric conversionefficiency, and responsivity of the photoelectric conversion elementwere evaluated on the basis of the sample 6. In an experimental example4-3, a photoelectric conversion element that included an organicphotoelectric conversion layer using, as the third organic semiconductormaterial, a material (the formula (7)) having a lower HOMO level than aHOMO level of the second organic semiconductor material was fabricated(a sample 43), and spectroscopic characteristics, photoelectricconversion efficiency, and responsivity of the photoelectric conversionelement were evaluated on the basis of the sample 6. The compositionsand evaluation of the respective samples in the respective experimentalexamples are summarized in Table 7.

TABLE 7 Organic Photoelectric Characteristic Conversion LayerParticularly First Second Third Spectroscopic Inferior to Kind Kind KindShape EQE Responsivity Example Experimental Sample 61 Formula FormulaFormula Narrow 1.00 1.0 — Example 4-1 (1-1) (6-3) (3-2) 20%   40%   40%Sample 40 Formula Formula Formula Narrow 1.00 0.9 — (1-1) (6-3) (3-2)35% 32.5% 32.5% Sample 41 Formula Formula Formula Board 1.00 0.9Spectroscopic (1-1) (6-3) (3-2) Shape 40%   30%   30% ExperimentalSample 6 Formula Formula Formula Narrow 1.00 1.0 — Example 4-2 (1-1)(6-3) (3-2) 25% 37.5% 37.5% Sample 42 Formula Formula Formula Board 0.102.0 Spectroscopic (1-1) (4-2) (5-1) Shape, EQE 25% 37.5% 37.5%Experimental Sample 6 Formula Formula Formula Narrow 1.00 1.0 — Example4-3 (1-1) (6-3) (3-2) 25% 37.5% 37.5% Sample 43 Formula Formula FormulaNarrow 0.60 10.0 Response (1-1) (6-3) (7) Speed 25% 37.5% 37.5%

As can be seen from results in the experimental example 4-1, in order tokeep a sharp spectroscopic shape, the composition ratio of the firstorganic semiconductor material was desirably less than 40%. As can beseen from results in the experimental example 4-2, in order to achieve asharp spectroscopic shape and high EQE, the second organic semiconductormaterial in the form of the single-layer film desirably had a higherlinear absorption coefficient of the maximal absorption wavelength inthe visible light region than each of the single-layer film of the firstorganic semiconductor material and the single-layer film of the thirdorganic semiconductor material. As can be seen from results in theexperimental example 4-3, in order to achieve high response speed, asthe third organic semiconductor material, a material having a HOMO levelequal to or higher than the HOMO level of the second organicsemiconductor material was desirably selected.

Experiment 5: Regarding Third Organic Semiconductor Material

In an experimental example 5, C60 (the formula (1-1)) as the firstorganic semiconductor material (the first kind), SubPcOCl (the formula(6-2)) as the second organic semiconductor material (the second kind),and QD (the formula (3-1)) as the third organic semiconductor material(the third kind) were used to fabricate a photoelectric conversionelement (a sample 56) having a 1-mm by 1-mm photoelectric conversionregion with use of a method similar to that in the foregoing experiment3. Moreover, as samples 57 and 58, photoelectric conversion elementshaving the same configuration as that of the sample 56, except that αNPD(the formula (4-2); the sample 57) and rubrene (the formula (8); thesample 58) were used in place of QD. Spectroscopic characteristics, thephotoelectric conversion efficiency, and responsivity of these samples56 to 58 were evaluated, and results of the evaluation were summarizedin Table 8.

TABLE 8 Organic Photoelectric Conversion Layer First Second ThirdSpectroscope Respon- Kind Kind Kind Shape EQE sivity Sample 56 FormulaFormula Formula Narrow 1.00 1.0 (1-1) (6-2) (3-1) 25% 37.5% 37.5% Sample57 Formula Formula Formula Narrow 0.30 5.0 (1-1) (6-2) (9) 25% 37.5%37.5% Sample 58 Formula Formula Formula Narrow 0.13 30.0  (1-1) (6-2)(8) 25% 37.5% 37.5%

In the present experiment, the sample 56 using QD as the third organicsemiconductor material exhibited the most favorable values in bothresponsivity and EQE. Subsequently, the sample 57 using αNPD as thethird organic semiconductor material exhibited favorable values in bothresponsivity and EQE. In the sample 58 using rubrene, the values ofresponsivity and EQE were lower than those in the samples 56 and 57. Itis understood that, a reason regarding responsivity is that an organicsemiconductor material including a hetero element (herein, QD and αNPD)has a property of easily maintaining higher electric charge (inparticular, hole) mobility than an organic semiconductor materialincluding carbon and hydrogen (herein, rubrene). It is understood that areason regarding EQE is that excitons generated through light absorptionare separated more efficiently at an interface formed by the organicsemiconductor material including a hetero element and any other organicsemiconductor material than at an interface formed by the organicsemiconductor material including carbon and hydrogen and any otherorganic semiconductor material. This indicates that an organicsemiconductor material including a hetero element in a molecule of theorganic semiconductor material is preferably used as the third organicsemiconductor material. Moreover, this indicates that an organicsemiconductor material including a chalcogen element in a molecule ofthe organic semiconductor material is more preferable. Further, thisindicates that an organic semiconductor material including a heteroelement in a ring is more preferable.

Although the description has been given by referring to the embodiment,the modification examples, and the examples, the contents of the presentdisclosure are not limited to the embodiment, the modification examples,and the examples, and may be modified in a variety of ways. For example,the foregoing embodiment has exemplified, as the photoelectricconversion element (the solid-state imagine device), a configuration inwhich the organic photoelectric converter 11G detecting green light andthe inorganic photoelectric converters 11B and 11R respectivelydetecting blue light and red light are stacked; however, the contents ofthe present disclosure is not limited thereto. More specifically, theorganic photoelectric converter may detect red light or blue light, andthe inorganic photoelectric converter may detect green light.

Moreover, the number of organic photoelectric converters, the number ofinorganic photoelectric converters, a ratio between the organicphotoelectric converters and the inorganic photoelectric converters arenot limited, and two or more organic photoelectric converters may beprovided, or color signals of a plurality of colors may be obtained byonly the organic photoelectric converter. Further, the contents of thepresent disclosure is not limited to a configuration in which organicphotoelectric converters and inorganic photoelectric converters arestacked along the vertical direction, and organic photoelectricconverters and inorganic photoelectric converters may be disposed sideby side along a substrate surface.

Furthermore, the foregoing embodiment has exemplified the configurationof the back-side illumination type solid-state imaging device; however,the contents of the present disclosure are applicable to a front-sideillumination type solid-state imaging device. Further, it may not benecessary for the solid-state imaging device (the photoelectricconversion element) of the present disclosure to include all componentsdescribed in the foregoing embodiment, and the solid-state imagingdevice of the present disclosure may include any other layer.

Note that the effects described herein are illustrative andnon-limiting, and effects to be achieved by the present disclosure maybe effects other than those described herein.

It is to be noted that the present technology may have the followingconfigurations.

[1]

A photoelectric conversion element, including:

a first electrode and a second electrode facing each other; and

a photoelectric conversion layer provided between the first electrodeand the second electrode, and including a first organic semiconductormaterial, a second organic semiconductor material, and a third organicsemiconductor material that have mother skeletons different from oneanother,

the first organic semiconductor material being one of fullerenes andfullerene derivatives,

the second organic semiconductor material in a form of a single-layerfilm having a higher linear absorption coefficient of a maximal lightabsorption wavelength in a visible light region than a single-layer filmof the first organic semiconductor material and a single-layer film ofthe third organic semiconductor material, and

the third organic semiconductor material having a value equal to orhigher than a HOMO level of the second organic semiconductor material.

[2]

The photoelectric conversion element according to [1], in which thethird organic semiconductor material in a form of a single-layer filmhas higher hole mobility than hole mobility of a single-layer film ofthe second organic semiconductor material.

[3]

The photoelectric conversion element according to [1] or [2], in whichin the photoelectric conversion layer, excitons generated through lightabsorption by the second organic semiconductor material are separated atan interface between two organic semiconductor materials selected fromthe first organic semiconductor material, the second organicsemiconductor material, and the third organic semiconductor material.

[4]

The photoelectric conversion element according to any one of [1] to [3],in which the photoelectric conversion layer has a maximal absorptionwavelength in a range from 450 nm to 650 nm both inclusive.

[5]

The photoelectric conversion element according to any one of [1] to [4],wherein the third organic semiconductor material includes a heteroelement other than carbon (C) and hydrogen (H) in a molecule of thethird organic semiconductor material.

[6]

The photoelectric conversion element according to any one of [1] to [5],in which the photoelectric conversion layer includes the first organicsemiconductor material in a range from 10 vol % to 35 vol % bothinclusive.

[7]

The photoelectric conversion element according to any one of [1] to [6],in which the photoelectric conversion layer includes the second organicsemiconductor material in a range from 30 vol % to 80 vol % bothinclusive.

[8]

The photoelectric conversion element according to any one of [1] to [7],in which the photoelectric conversion layer includes the third organicsemiconductor material in a range from 10 vol % to 60 vol % bothinclusive.

[9]

The photoelectric conversion element according to any one of [1] to [8],in which one of the second organic semiconductor material and the thirdorganic semiconductor material is a quinacridone derivative representedby the following formula (1):

where each of R1 and R2 is independently one of a hydrogen atom, analkyl group, an aryl group, and a heterocyclic group, each of R3 and R4is independently one of an alkyl chain, an alkenyl group, an alkynylgroup, an aryl group, a cyano group, a nitro group, and a silyl group,and two or more of R3 or two or more of R4 optionally form a ringtogether, and each of n1 and n2 is independently 0 or an integer of 1 ormore.

[10]

The photoelectric conversion element according to any one of [1] to [8],in which one of the second organic semiconductor material and the thirdorganic semiconductor material is one of a triallylamine derivativerepresented by the following formula (3) and a benzothienobenzothiophenederivative represented by the following formula (4):

where each of R20 to R23 is independently a substituent represented by aformula (2)′, each of R24 to R28 is independently one of a hydrogenatom, a halogen atom, an aryl group, an aromatic hydrocarbon ring group,an aromatic hydrocarbon ring group having an alkyl chain or asubstituent, an aromatic heterocyclic group, and an aromaticheterocyclic group having an alkyl chain or a substituent, adjacent onesof R24 to R28 are optionally saturated or unsaturated divalent groupsthat are bound to one another to form a ring, and

where each of R5 and R6 is independently one of a hydrogen atom and asubstituent represented by a formula (3)′, and R7 is one of an aromaticring group and an aromatic ring group having a substituent.

[11]

The photoelectric conversion element according to any one of [1] to [8],in which one of the second organic semiconductor material and the thirdorganic semiconductor material is a subphthalocyanine derivativerepresented by the following formula (4):

where each of R8 to R19 is independently selected from a groupconfigured of a hydrogen atom, a halogen atom, a straight-chain,branched, or cyclic alkyl group, a thioalkyl group, a thioaryl group, anarylsulfonyl group, an alkylsulfonyl group, an amino group, analkylamino group, an arylamino group, a hydroxy group, an alkoxy group,an acylamino group, an acyloxy group, a phenyl group, a carboxy group, acarboxyamide group, a carboalkoxy group, an acyl group, a sulfonylgroup, a cyano group, and a nitro group, any adjacent ones of R8 to R19are optionally part of a condensed aliphatic ring or a condensedaromatic ring, the condensed aliphatic ring or the condensed aromaticring optionally includes one or more atoms other than carbon, M is oneof boron and a divalent or trivalent metal, and X is an anionic group.

[12]

The photoelectric conversion element according to any one of [1] to [9]and [11], in which the second organic semiconductor material is asubphthalocyanine derivative, and the third organic semiconductormaterial is a quinacridone derivative.

[13]

The photoelectric conversion element according to any one of [1] to [8],[10], and [11], in which the second organic semiconductor material is asubphthalocyanine derivative, and the third organic semiconductormaterial is a triallylamine derivative or a benzothienobenzothiophenederivative.

[14]

The photoelectric conversion element according to any one of [1] to[13], in which the fullerenes and the fullerene derivatives arerepresented by one of the following formulas (5) and (6):

where each R is independently one of a hydrogen atom, a halogen atom, astraight-chain, branched, or cyclic alkyl group, a phenyl group, a grouphaving a straight-chain or condensed ring aromatic compound, a grouphaving a halide, a partial fluoroalkyl group, a perfluoroalkyl group, asilylalkyl group, a silyl alkoxy group, an arylsilyl group, anarylsulfanyl group, an alkylsulfanyl group, an arylsulfonyl group, analkylsulfonyl group, an arylsulfide group, an alkylsulfide group, anamino group, an alkylamino group, an arylamino group, a hydroxy group,an alkoxy group, an acylamino group, an acyloxy group, a carbonyl group,a carboxy group, a carboxyamide group, a carboalkoxy group, an acylgroup, a sulfonyl group, a cyano group, a nitro group, a group having achalcogenide, a phosphine group, a phosphone group, and derivativesthereof, and each of “n” and “m” is 0 or an integer of 1 or more.

[15]

The photoelectric conversion element according to any one of [1] to[14], in which the photoelectric conversion layer includes a fourthorganic semiconductor material having the same mother skeleton as themother skeleton of one of the first organic semiconductor material, thesecond organic semiconductor material, and the third organicsemiconductor material, and having a different substituent.

[16]

The photoelectric conversion element according to any one of [1] to[15], in which the visible light region is in a range from 450 nm to 800nm both inclusive.

[17]

A solid-state imaging device provided with pixels each including one ormore organic photoelectric converters, each of the organic photoelectricconverters including:

a first electrode and a second electrode facing each other; and

a photoelectric conversion layer provided between the first electrodeand the second electrode, and including a first organic semiconductormaterial, a second organic semiconductor material, and a third organicsemiconductor material that have mother skeletons different from oneanother,

the first organic semiconductor material being one of fullerenes andfullerene derivatives,

the second organic semiconductor material in a form of a single-layerfilm having a higher linear absorption coefficient of a maximal lightabsorption wavelength in a visible light region than a single-layer filmof the first organic semiconductor material and a single-layer film ofthe third organic semiconductor material, and

the third organic semiconductor material having a value equal to orhigher than a HOMO level of the second organic semiconductor material.

[18]

The solid-state imaging device according to [17], in which the one ormore organic photoelectric converters, and one or more inorganicphotoelectric converters that performs photoelectric conversion in awavelength region different from a wavelength region of the organicphotoelectric converters are stacked in each of the pixels.

[19]

The solid-state imaging device according to [18], in which

the one or more inorganic photoelectric converters are formed to beembedded in a semiconductor substrate, and

the one or more organic photoelectric converters are formed on firstsurface side of the semiconductor substrate.

[20]

The solid-state imaging device according to [19], in which

the one or more organic photoelectric converters perform photoelectricconversion on green light, and

an inorganic photoelectric converter that performs photoelectricconversion on blue light and an inorganic photoelectric converter thatperforms photoelectric conversion on red light are stacked in thesemiconductor substrate.

This application is based upon and claims the benefit of priority ofJapanese Patent Application No. 2015-110900 filed in the Japan PatentOffice on May 29, 2015 and Japanese Patent Application No. 2016-072197filed in the Japan Patent Office on Mar. 31, 2016, the entire contentsof which are incorporated herein by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

The invention claimed is:
 1. A photoelectric conversion element,comprising: a first electrode and a second electrode facing each other;and a photoelectric conversion layer provided between the firstelectrode and the second electrode, and including a first organicsemiconductor material, a second organic semiconductor material, and athird organic semiconductor material that have mother skeletonsdifferent from one another, wherein the first organic semiconductormaterial is one of fullerenes and fullerene derivatives, wherein thesecond organic semiconductor material is formed as a single-layer filmhaving a maximal light absorption wavelength in a visible light regionin a range from 500 nm to 600 nm both inclusive, and wherein the thirdorganic semiconductor material is formed as a single-layer film having ahigher hole mobility than a hole mobility of the single-layer film ofthe second organic semiconductor material.
 2. The photoelectricconversion element according to claim 1, wherein the second organicsemiconductor material has the maximal light absorption wavelength inthe visible light region in a range from 550 nm to 600 nm bothinclusive.
 3. The photoelectric conversion element according to claim 2,wherein the second organic semiconductor material has the maximal lightabsorption wavelength in the visible light region in a range from 560 nmto 590 nm both inclusive.
 4. The photoelectric conversion elementaccording to claim 1, wherein a linear absorption coefficient of themaximal light absorption wavelength in the visible light region of thesecond organic semiconductor material is higher than 1.5×10⁵ cm⁻¹. 5.The photoelectric conversion element according to claim 4, wherein thelinear absorption coefficient of the maximal light absorption wavelengthin the visible light region of the second organic semiconductor materialis higher than 2.0×10⁵ cm⁻¹.
 6. The photoelectric conversion elementaccording to claim 5, wherein the linear absorption coefficient of themaximal light absorption wavelength in the visible light region of thesecond organic semiconductor material is higher than 3.0×10⁵ cm⁻¹. 7.The photoelectric conversion element according to claim 6, wherein thelinear absorption coefficient of the maximal light absorption wavelengthin the visible light region of the second organic semiconductor materialis higher than 3.3×10⁵ cm⁻¹.
 8. The photoelectric conversion elementaccording to claim 1, wherein a linear absorption coefficient of themaximal light absorption wavelength in the visible light region of thesecond organic semiconductor material is higher than ten times a linearabsorption coefficient of a 450 nm wavelength of the second organicsemiconductor material.
 9. The photoelectric conversion elementaccording to claim 8, wherein the linear absorption coefficient of themaximal light absorption wavelength in the visible light region of thesecond organic semiconductor material is higher than twenty times thelinear absorption coefficient of the 450 nm wavelength of the secondorganic semiconductor material.
 10. The photoelectric conversion elementaccording to claim 1, wherein a linear absorption coefficient of themaximal light absorption wavelength in the visible light region of thesecond organic semiconductor material is higher than three times alinear absorption coefficient of a 500 nm wavelength of the secondorganic semiconductor material.
 11. The photoelectric conversion elementaccording to claim 1, wherein a linear absorption coefficient of themaximal light absorption wavelength in the visible light region of thesecond organic semiconductor material is higher than fifteen times alinear absorption coefficient of a 625 nm wavelength of the secondorganic semiconductor material.
 12. The photoelectric conversion elementaccording to claim 1, wherein the first organic semiconductor materialis fullerenes.
 13. The photoelectric conversion element according toclaim 12, wherein the first organic semiconductor material is C60fullerene.
 14. The photoelectric conversion element according to claim12, wherein the first organic semiconductor material is C70 fullerene.15. The photoelectric conversion element according to claim 12, whereinthe first organic semiconductor material is C60 fullerene and C70fullerene.
 16. The photoelectric conversion element according to claim1, wherein in the photoelectric conversion layer, excitons generatedthrough light absorption by the second organic semiconductor materialare separated at an interface between two organic semiconductormaterials selected from the first organic semiconductor material, thesecond organic semiconductor material, and the third organicsemiconductor material.
 17. The photoelectric conversion elementaccording to claim 1, wherein the photoelectric conversion layer has amaximal absorption wavelength in a range from 450 nm to 650 nm bothinclusive.
 18. The photoelectric conversion element according to claim1, wherein the third organic semiconductor material includes a heteroelement other than carbon (C) and hydrogen (H) in a molecule of thethird organic semiconductor material.
 19. The photoelectric conversionelement according to claim 1, wherein the photoelectric conversion layerincludes the first organic semiconductor material in a range from 10 vol% to 35 vol % both inclusive.
 20. The photoelectric conversion elementaccording to claim 1, wherein the photoelectric conversion layerincludes the second organic semiconductor material in a range from 30vol % to 80 vol % both inclusive.
 21. The photoelectric conversionelement according to claim 1, wherein the photoelectric conversion layerincludes the third organic semiconductor material in a range from 10 vol% to 60 vol % both inclusive.
 22. The photoelectric conversion elementaccording to claim 1, wherein one of the second organic semiconductormaterial and the third organic semiconductor material is a quinacridonederivative represented by the following formula (1):

where each of R1 and R2 is independently one of a hydrogen atom, analkyl group, an aryl group, and a heterocyclic group, each of R3 and R4is independently one of an alkyl chain, an alkenyl group, an alkynylgroup, an aryl group, a cyano group, a nitro group, and a silyl group,and two or more of R3 or two or more of R4 optionally form a ringtogether, and each of n1 and n2 is independently 0 or an integer of 1 ormore.
 23. The photoelectric conversion element according to claim 1,wherein one of the second organic semiconductor material and the thirdorganic semiconductor material is one of a triarylamine derivativerepresented by the following formula (2) and a benzothienobenzothiophenederivative represented by the following formula (3):

where each of R20 to R23 is independently a substituent represented by aformula (2)′, each of R24 to R28 is independently one of a hydrogenatom, a halogen atom, an aryl group, an aromatic hydrocarbon ring group,an aromatic hydrocarbon ring group having an alkyl chain or asubstituent, an aromatic heterocyclic group, and an aromaticheterocyclic group having an alkyl chain or a substituent, adjacent onesof R24 to R28 are optionally saturated or unsaturated divalent groupsthat are bound to one another to form a ring, and

where each of R5 and R6 is independently one of a hydrogen atom and asubstituent represented by a formula (3)′, and R7 is one of an aromaticring group and an aromatic ring group having a substituent.
 24. Thephotoelectric conversion element according to claim 1, wherein one ofthe second organic semiconductor material and the third organicsemiconductor material is a subphthalocyanine derivative represented bythe following formula (4):

where each of R8 to R19 is independently selected from a groupconsisting of a hydrogen atom, a halogen atom, a straight-chain,branched, or cyclic alkyl group, a thioalkyl group, a thioaryl group, anarylsulfonyl group, an alkylsulfonyl group, an amino group, analkylamino group, an arylamino group, a hydroxy group, an alkoxy group,an acylamino group, an acyloxy group, a phenyl group, a carboxy group, acarboxyamide group, a carboalkoxy group, an acyl group, a sulfonylgroup, a cyano group, and a nitro group, any adjacent ones of R8 to R19are optionally part of a condensed aliphatic ring or a condensedaromatic ring, the condensed aliphatic ring or the condensed aromaticring optionally includes one or more atoms other than carbon, M is oneof boron and a divalent or trivalent metal, and X is an anionic group.25. The photoelectric conversion element according to claim 1, whereinthe second organic semiconductor material is a subphthalocyaninederivative, and the third organic semiconductor material is aquinacridone derivative.
 26. The photoelectric conversion elementaccording to claim 1, wherein the second organic semiconductor materialis a subphthalocyanine derivative and the third organic semiconductormaterial is a triarylamine derivative or a benzothienobenzothiophenederivative.
 27. The photoelectric conversion element according to claim1, wherein the fullerenes and the fullerene derivatives are representedby one of the following formulas (5) and (6):

where each R is independently one of a hydrogen atom, a halogen atom, astraight-chain, branched, or cyclic alkyl group, a phenyl group, a grouphaving a straightchain or condensed ring aromatic compound, a grouphaving a halide, a partial fluoroalkyl group, a perfluoroalkyl group, asilylalkyl group, a silyl alkoxy group, an arylsilyl group, anarylsulfanyl group, an alkylsulfanyl group, an arylsulfonyl group, analkylsulfonyl group, an arylsulfide group, an alkylsulfide group, anamino group, an alkylamino group, an arylamino group, a hydroxy group,an alkoxy group, an acylamino group, an acyloxy group, a carbonyl group,a carboxy group, a carboxyamide group, a carboalkoxy group, an acylgroup, a sulfonyl group, a cyano group, a nitro group, a group having achalcogenide, a phosphine group, a phosphone group, and derivativesthereof, and each of “n” and “m” is 0 or an integer of 1 or more. 28.The photoelectric conversion element according to claim 1, wherein thephotoelectric conversion layer includes a fourth organic semiconductormaterial having a same mother skeleton as a mother skeleton of one ofthe first organic semiconductor material, the second organicsemiconductor material, and the third organic semiconductor material,and having a different substituent.
 29. The photoelectric conversionelement according to claim 1, wherein the visible light region is in arange from 450 nm to 800 nm both inclusive.
 30. A solid-state imagingdevice provided with pixels each including one or more organicphotoelectric converters, each of the one or more organic photoelectricconverters comprising: a first electrode and a second electrode facingeach other; and a photoelectric conversion layer provided between thefirst electrode and the second electrode, and including a first organicsemiconductor material, a second organic semiconductor material, and athird organic semiconductor material that have mother skeletonsdifferent from one another, the first organic semiconductor materialbeing one of fullerenes and fullerene derivatives, the second organicsemiconductor material formed as a single-layer film having a maximallight absorption wavelength in a visible light region in a range from500 nm to 600 nm both inclusive, and the third organic semiconductormaterial formed as a single-layer film having a higher hole mobilitythan a hole mobility of the single-layer form of the second organicsemiconductor material.
 31. The solid-state imaging device according toclaim 30, wherein the one or more organic photoelectric converters, andone or more inorganic photoelectric converters that performsphotoelectric conversion in a wavelength region different from awavelength region of the one or more organic photoelectric convertersare stacked in each of the pixels.
 32. The solid-state imaging deviceaccording to claim 31, wherein the one or more inorganic photoelectricconverters are embedded in a semiconductor substrate, and the one ormore organic photoelectric converters are formed on a first surface sideof the semiconductor substrate.
 33. The solid-state imaging deviceaccording to claim 32, wherein one of the one or more organicphotoelectric converters performs photoelectric conversion on greenlight, and one of the one or more inorganic photoelectric convertersperforms photoelectric conversion on blue light or red light.
 34. Anelectronic apparatus, comprising: an optical lens; a signal processor;and a solid-state imaging device provided with pixels each including oneor more organic photoelectric converters, each of the one or moreorganic photoelectric converters comprising: a first electrode and asecond electrode facing each other; and a photoelectric conversion layerprovided between the first electrode and the second electrode, andincluding a first organic semiconductor material, a second organicsemiconductor material, and a third organic semiconductor material thathave mother skeletons different from one another, wherein the firstorganic semiconductor material is one of fullerenes and fullerenederivatives, wherein the second organic semiconductor material is formedas a single-layer film having a maximal light absorption wavelength in avisible light region in a range from 500 nm to 600 nm both inclusive,and wherein the third organic semiconductor material is formed as asingle-layer film having a higher hole mobility than a hole mobility ofthe single-layer film of the second organic semiconductor material.